The use-case is in the opposite direction: when I only have my phone, I have my entire computer with me - including the storage and the files and keys and so on.
No syncing required. You only have a single computer. That's a big win, I think ...
If you care about the stuff on that computer, you really want it synced somewhere anyway.
I don't personally see the utility in having my phone be my computer. I don't need Visual Studio or Photoshop on my phone. If I don't have my laptop/desktop, I'm not going to work on the things I typically do with a full-power computer. The phone is just not the right form factor, so it doesn't help for that stuff to be on my phone.
"If you care about the stuff on that computer, you really want it synced somewhere anyway."
I disagree.
If you care about (stuff) you really want to back it up somewhere.
This is different than "syncing" which can mean anything, is usually a completely unintelligible process for the end user, is fragile, and is actually a hard problem.[1]
Much more intelligible and manageable is to have one single repository of data and carry that "kernel" of stored data everywhere. Yes, certainly you should back it up, but the backup is just that: a point in time backup that you do not operate against.
[1] Two way sync, dealing with new, but different objects on both devices ... this is not a "solved" use-case ...
> This is different than "syncing" which can mean anything
Then we should probably define it before asserting that it's "completely unintelligible", "fragile", or a "hard problem", right? Yes, full multi-way sync is not a simple problem. Most scenarios don't need this (and even ones that do tend to devolve into simple cases since single-actor conflicts are not that common).
The simplest case for "sync" is just "my stuff is in the cloud". Call it remote storage, since sync is ambiguous. Make the client dumb, put the data online, and most of the complexity evaporates. Of course, local storage with remote backup is also a reasonable solution that has different tradeoffs.
For me personally, I prefer the "remote storage" solution for most things. I greatly appreciate that my email is just "magically" everywhere I need it to be without me carrying a repository of email in my pocket. I love that all my important documents and photos are accessible everywhere even if I forget my phone.