When it comes to a Windows installation Mame developers made the very sensible decision to bypass the registry. It uses old style coding, keeping configuration settings in .INI files. This is how all programs were back in the days of Windows 3.1. Mame is - and they'll probably laugh at me for saying it and I'm sure it's not entirely correct- essentially a DOS executable. The GUI is an add-on (I use GUI's, myself).
Because of this, each Mame installation is an instance within itself. If you specify a different install folder, you can install Mame as many times as you want, and maintain different versions too. I have three installed: .149, .160, and .164.
I don't leave it at that though. Some folders in a Mame installation can be shared. For example, I have three Mame installations in folders: Mame149, Mame160 and Mame164.
I then have another folder called: MameFolders. I have the artwork folder stored here, and I path each installation of Mame to it, rather than using the default (where it looks in the folder it's being run from).
The reason for this is is simple - if I have a new artwork Zip, as I did today with Disco No 1, then all I have to do is copy it to one place, the artwork folder under Mamefolders. Since all three of my Mame installations are pathed to this location, all three of them pick up the new artwork.
If I didn't do this, I'd have to copy the Zip to three different places, once for each installation.
I do the same for Snapshots, and a few other folders......