This folder behaves exactly the same as a Dropbox folder, anything stored in it will sync to all other macs that are logged onto the same iCloud account, there are no restrictions on what you can put into this folder.
To make this folder more usable you can either use third party tools or create a link to an area of your drive which you prefer.
If you want to keep it simple you have two options, add the Mobile Documents folder to the dock, or just create a symbolic link to an area of your drive that will make access easier for you, to do so just use the following command:
ln -s ~/Library/Mobile Documents ~/Desktop/SyncFolder
(just replace “SyncFolder” with the name you want to see on your folder)