By default, Windows grants limited permissions to all apps running, even if your account is an Administrator type. By limited permissions, this restricts access to certain locations in storage and RAM locations (basically, the RAM locations owned by the app and shared regions) as well as certain actions in the OS, like setting up user accounts or modifying services. This is to make sure that if the app has a problem or, the more likely reason for this, has malicious intent, it can't do much to the system itself.
For instance, if you ran ransomeware on limited permissions, it'll only be able to encrypt the files you normally have access to. It won't go and encrypt someone else's files if you have another user account on the computer because by default users can't access each other's user folder.
Running as an administrator grants basically unlimited permissions. So that app now has permission to access anything on the system or do anything it wants to the system (well, mostly). With regards to reliability, no, it doesn't increase the app's reliability. In fact, it could decrease overall system reliability if the app has a nasty bug in it.