Think of a Cloud Drive as an external hard drive attached to your computer by wi-fi + internet rather than wire. That's all it is. It behaves exactly like an eternal drive. You can treat it like an external drive: copy files to it, delete files on it, create sub-directories, even back it up. It has one huge advantage over a conventional external drive: it is not on your premises or in your possession, so it can't get taken away by anyone with or without a warrant, or soaked if the house floods, or melts in a fire, or lost if someone's kid spills their orange juice on it, or (enter description of disaster here).
We need to protect against four things: confiscation of our devices; loss of one or more devices; loss of specific data on our devices; loss of access to our Cloud account, and other Cloud-based services. We also need to handle backup of data across multiple devices, without creating a complicated and time-consuming backup routine. For some people, especially recording artists, photographers and videographers, handling large-scale data backup is part of the job, and I’m addressing the needs of people who generate smaller amounts of data.
A Cloud drive protects against losing devices, or having devices confiscated. It allows sharing between multiple devices, and usually offer a browser-based interface, allowing access from any device, as long as you remember the password. Most provide a thirty-day undelete facility to deal with stumble-thumb deletes.
Conventional hard disk backups protect against losing access to your Cloud drive account, or losing internet access. Restores or data-reading can be done to any device with a suitable data port, though if you used special software (e.g. to encrypt and compress) you will need that on the device.
Online backup services protect against loss of external hard drives and the Cloud drive.
(Professionals will usually use a Cloud drive, keeping local copies as storage allows, and use an online backup service - since they aren’t going to walk around making backups of individual employee’s laptops.)
You're already on the Cloud in so many ways. All the e-mail services keep your archives on their servers - in the Cloud. Your password manager keeps your vault in the Cloud. Apple Notes / Evernote and the others all store in the Cloud. All your social media is in the Cloud. Any product that offers multi-device access and syncing is cloud-based.
If you use music streaming, you are accessing a cloud-based music library - far bigger than anything the most obsessed audiophile could make. If you stream video, same thing.
It's the final step to put the documents, photographs, graphics and other files you create onto a drive in the Cloud. The Cloud application will create a directory on your device for its use, and anything you put in that directory will get copied up to the Cloud drive. You can tell the Cloud application you want to keep local copies, or that you are happy downloading from the Cloud drive as needed.
What gets stored in that local directory? The data I need to carry on my life, in case I lose everything in the same day (lose phone on the train, laptop stolen in the pub, dog eats the iPad... you know the kind of thing). Contact lists, schedules, programming code, drafts of novels / poems / textbooks, DAW files, reference books, my favourite photos, music tracks, videos, diary / journal, Notes app, and so on.
E-mails, contacts, appointments. On Gmail. Since 1891.
Text documents / Notes-style apps. Pffft. Doesn't matter how much I have, it likely is no more than 1 GB. Nobody can write that much in one lifetime.
PDFs and similar: Not really an issue. 3-4 GB at most for even the most avid reader. Stored in Books.
Music. No more ripping CDs into Apple Music and synching playlists to the phone. CD-quality streaming services are now affordable and allow downloading for off-line access. If I am actually going to be off-line: 5G and wireless coverage has expanded beyond anyone's wildest dreams in 2015. I keep my CDs (unless I really regret buying it), while Amazon and other downloaders keep track of what I bought from them, so the files are always there. I only really need to keep music files I downloaded or ripped, which can't be found elsewhere. That is remarkably few. (**)
(Qobuz subscribers: downloaded files are added to your Library, with a tick next to them.)
Photo / Video backup. A glance at Reddit suggests this is deeply personal: some people are hoarders and remind you that storage is cheap (which at £150 for at 5TB external SSD it is); while others are minimalists and do not want to spend time managing backups. Then there's a whole bunch of people between these extremes. I tend to the minimalist side. My intention is that Favourites and recent haven't-made-my-mind-up-yet shots will be in iCloud Photos, and everything else I don't throw out will be in directory that gets an external backup from time to time. There's a lot of prep required for this, which I'll talk about this in another post.
With my minimalist approach, I don't have a lot of data, so I get by on iCloud's 50GB plan. FLAC-ripping, RAW-shooting, Lightroom-editing, keep-everything maximalists, will be looking at least at 2TB or more. After making use of the 1TB Adobe throw in with Lightroom subscriptions. That starts to cost.
Bonus Topic: sharing across devices. One benefit of Cloud drives is that all your Windows / iOS / OS X devices can access the drives, but sharing is not compulsory. Apple devices can be customised app by app. How much you do depends on how much you trust the other people who can use your devices, and I'll let you think through how much you trust the kids not to accidentally delete photos or mail stuff to their friends. I let Files access everything it can, and share my Photos on the phone, iPad and laptop. My music apps (Sonos, Qobuz, Amazon, Apple Music) are on all my iOS devices, and I can access those services through a browser on the laptop. I don't have Books on the phone, because I can't read on it. I can get Mail and Contacts via any browser, and share the Calendar.
Bonus bonus topic: internet privacy. I'm all for someone from Apple, Microsoft, the NSA, Five Eyes (or Five Guys, for that matter) reading my thoughts and looking at my snapshots. They might learn something. You're welcome.
(*) Having all your equipment and backup drives taken away because you made a mean tweet, or one of your darling children downloaded instructions to make an atomic bomb, or a dodgy mate sent you a dodgy image, or whatever happens to be illegal these days. They can take your devices, but they can't stop you looking at your data if you can get at it.
(**) A while ago there was a fad for ripping all one's CDs and then throwing them away. Because shelf space or something. I ripped everything to AAC / MP3 because it was the only way to download it to the music player / phone. Hence the need to backup music libraries. To become really useful, streaming services needed a) large libraries, b) CD-quality at £10 / month, c) reliable hi-speed internet and wireless, d) high-quality DAC chipsets at commodity prices. This only really came together in 2020.