Cloud & local storage clarification


I think i still have some doubts about using iCloud (sorry for asking first here instead of finding in Apple’s doc).

As the Documents directory is automatically backed up to iCloud (unless disabled in Setting for the app), if you explicitly store the DB transaction log in iCloud as in this chapter, you always should mark the actual DB files (except for the log) to not be synchronized with iCloud (and they still can reside either in the ubiquitous dir or in Documents (of course here it can be problematic if more iCloud users use the app on the same device)).
Otherwise, you manually put the transaction log to the iCloud ubiq. dir. and also the other DB files are synchronized, you are a) wasting space and bandwidth and b) perhaps it can cause some problems (both DB parts can be changed remotely from the cloud).

Am I correct?

If I am too lazy and don’t want to implement any iCloud synchro by myself, can I just rely on the automatic iCloud backup of the Documents dir? Is it a bidirectional synchro to iCloud and then also back to all other iOS devices? (I have only 1 iPhone, so can’t try it…). If it’s bi. synchro, is the app being somehow notified about that the synchro from iCloud to the device happened?
I guess in this case it will be just a backup to the cloud for the given user-device-app. Right?

Thanks a lot!