Randomised Monsters

I haven’t exactly done this, because I always choose monsters based on the environment and story. I did “balance” an encounter based solely on the number of minis I had available. I just kept throwing gnolls at the table until I ran out and said “this is what you see.” Provided your players were high enough level and you had quick access to the statblocks, there are worse ways of populating dungeons than random handfuls of miniatures. It’s no worse than how some of the dungeons in Against the Giants seem to have been populated…

5th Edition works quite well for this, as a horde lower level monsters can still serve as a threat. This was much more limited in 4e and 3e, as low level monsters quickly lost the ability to reliably hit after a couple levels.