Does uninstalling and installing a MacOS App Store App do anything? I have some issue with a Mac OS application that I got from the App Store. The support suggested to uninstall the app and install it again.  My question is: Is there any way this can help? 

There is a separation of programs and user data in MacOS, so uninstalling the program and reinstalling it should be no-op in total. Is it?
It should be. It won't delete any of your documents, but you might want to back up these locations, if they exist:


~/Library/Preferences/com.whatever.appname.plist
~/Library/Application Support/AppName


You almost certainly don't need to do this--I don't know what exactly the App Store uninstall process does--but it doesn't hurt to be safe.

Update: Due to sandboxing, you won't find anything in either of these locations. (All apps from the App Store are sandboxed, but apps you get somewhere else probably aren't.) You should look here instead:


~/Library/Containers/com.whatever.appname