I dread helping anyone with iTunes related issues. The syncing process is dangerous, it's far too easy to wipe someone's collection of music / family photos / pictures. I'm not sure if this is an isolated issue but I start sweating bullets as soon as I have to connect an iDevice to iTunes. What really shocks me is that instead of showing a big red warning message before a destructive sync, it silently goes ahead and wipes data without even asking. And there's no easy way to tell what a sync is going to do. After any iTunes sync I generally think "Ok, now let's assess the damage".
To add insult to injury it's almost impossible to make a file-for-file backup before decimating a device with iTunes sync. In fact, the iTunes sync process is the main reason I stick to Android despite it having a whole other ecosystem of flaws. I'll take a USB Mass storage device and robocopy / rsync, thanks. They actually work.
I never understood this. You keep all your music in iTunes. What harm could possibly come even if it did accidentally wipe your device? The worst possible scenario is that you'll have to wait a few minutes to sync it back again.
Not an iTunes user, but I guess some people just want to do a selective sync to certain devices to keep storage use in check and maintain library navigability on the device. That can be quite a bit of work which you wouldn't want to lose to technical failure.
The "correct" way to do this is to make a playlist of the things you want on your device, and then to tell iTunes to sync to that playlist (or collection of playlists) only.
My personal fear is losing my photos when performing a sync. iCloud tops out at 5GB, which you can't effectively manage.
It's far safer to plug your phone into a Windows machine and using the file system GUI to copy the photos to the folder you want. Using Preview to import the photos as if the iPhone is a scanner is another safe method.
The multiple user/multiple computer problem that you're referencing can probably be solved by logging in to the corresponding icloud account on the computer.
The free iCloud tops out at 5GB (which is low for storing device backups and photos; ideally, you should get the same storage as your device size for free). You can pay for more storage.
And if you don't want to trust iCloud with photo sync, there are other options (Dropbox does that, and Plex has a photo sync function if you want to host those files yourself).
To add insult to injury it's almost impossible to make a file-for-file backup before decimating a device with iTunes sync. In fact, the iTunes sync process is the main reason I stick to Android despite it having a whole other ecosystem of flaws. I'll take a USB Mass storage device and robocopy / rsync, thanks. They actually work.