Sven Seebeck has taken inspiration from Charles Choi and implemented a transient to ease one of his frequent operations. That task was playing music with EMMS. His needs, he says, are pretty vanilla. He typically just wants to play an album or perhaps a specific track from an album. He’s not concerned with playlists.
He cleverly let Dired do most of the heavy lifting. by opening a Dired buffer to his music repository, he get a listing of the albums and by selecting an album, the songs in it. The rest is pretty simple as you can see by looking at his code. It’s very easy to follow and understand.
The point here is not to highlight yet another transient menu: they’re simple enough that anyone can write one simply by following, say, Seebeck’s example. Rather, the point is, once, again, how the flexibility of Emacs allows you to do this sort of thing quickly and easily.