Yeah, I've not used the "auto" features to that extent, but I've DJ'ed at a few events and festivals just for fun and it's super convenient to have software that has analyzed my music library for BPM and key. I still get to play whatever I want to play, but if I'm drawing a blank or just looking for inspiration, I can sort by all tracks within "n" BPM of the current track and in the same/compatible key.

Then if I really want to play something that wouldn't normally fit with an easy transition, I can always adjust they key or tempo on the fly. There are limits before it starts to sound weird, but that can also be a neat way to mess with a song. Add a riff or a phrase from one song into the current one, but only because I'm able to halve the speed or chop up the time signature to match.

And that's just me as a barely fluent hobbyist. Experienced DJs can do some great stuff. Even a non-"mixing" DJ like a radio DJ can string together songs based on thematic connections, sneaky relations between artist or lyric or even the conditions in the room. Those can be a lot of fun and would be a lot harder to automate than simple beat matching.