Automation is good and it works like a charm with 15-20 min of editing, but it's not always possible to do it. I've got 3 examples where it's not usable.
The first one is if you don't have a single vocal track: I've been recording live acoustic music and specifically asked not to mic every single musician, that means you end up, hopefully, with a decent stereo track that you can't just automate. There goes your deesser or even your MS multiband.
The second example is the guy I used to work for 15 years ago used to deess the reverbs of the voices, and with very good results too. He used 902s for that.
And lastly, when you have plugins with massive amount of delay (UAD for example), in PT you end up having your volume automation way off your wave overview, so that automating becomes more of an annoyance. That is, if you deess post plugins, which is what I usually do.
As for using deesser for not only deessing, that's cool, I've used it on harsh sounding slapped bass lines, or on fingers-moving-on-strings sound on acoustic guitars an such, very useful.