Managed WordPress web hosts typically do nightly backups. That’s a great start however if something is important you should have multiple backups. My secondary backup method is a daily script which runs on a Backupsy VPS with lots of storage. There are two parts to the script. First an incremental sync download each WordPress site. Secondly an incrementally sync upload each WordPress site to cloud storage provider. Recently I changed my cloud storage from Dropbox over to B2 Cloud Storage.
Dropbox price changes and drops legacy features
With Dropbox I was running into a number of performance issues with their new v2 API. There is also an annoying limitation with their API which makes it impossible to restore a revision which has been changed more then a certain number of times. That's unfortunate as my Dropbox account has their legacy unlimited revisions. That means there is literally GBs of revisions data completely inaccessible from me. Dropbox is in transition. They are doing a good job at annoying heavy users like me.
Better to pay per usage if your a heavy user
Alternatives like Amazon S3 and B2 Cloud Storage offer unlimited storage within a pay per usage model. They love heavy users. B2 is a newer storage option made by the backup company Backblaze. Turns out it's not only cheaper then S3 but way easier to use.
B2 way faster then Dropbox
Every night my backup script syncs around 20GBs of changed files. With Dropbox this would frequently take all day to complete due to issues with their API. With B2 this will often complete within 6hrs. B2's API is a lot more developed then Dropbox and has no issues reaching any number of old revisions.