You had to directly over write the files in the program folder and reinstall to play another mod. You also could have made a copy of the folder and over written the files for different mods into a different folder.

I bet that was difficult! I'm glad the Mod Manager came out!

Difficult? Nah, just a bit more time consuming, depending on the speed of one's hdds.

The problem wasn't that we had to overwrite the files. I'd argue that you could probably copy and overwrite files faster than FLMM does it, however, where FLMM excels is the fact that it makes backups so you can quickly change between mods. Before FLMM, reverting was a pain, usually involved a reinstall.