Main benefits are that they are fairly easy to adjust so that you have a solid connection to your pedal yet still release it easily if you have things adjusted properly.

If you're using clips and straps, release can be a bit more difficult than a clipless pedal that's set up to release fairly easily.

Some track racers use clipless WITH straps, cuz unexpectedly clipping out sucks, and some track sprinters are pretty good at making that happen.