I was a demon slide guitarist for a long time, then not, then again thnx to Sonny Landreth. Butch Trucks is about the only guy crazy enough to learn to play jazz tunes in the right keys on slide; for everybody else, you accept the boundaries of each given tuning and poke around in the corners - write material that uses the streghts not the weaknesses. And for all that, I have found 24 frets to be useful.
The correct "harmonic placement" of pickups under the 24th fret node is a zeirdo, because strings vibrate the
least at the nodes. And, then, you fret them? But from the anguished faces made by the MTV-trained generation, you'd think that having "only" 21 or 22 frets was an
advantage because you then get to make a face like you're passing a Mark II torpedo (made of pepperoni)* every time you bend a .009" string three frets. OOOOOH.... OOOOOOH...
Plop!
And on the other hand, apparently the only way to get a guitar with enough of a cutaway that you can use fingerings with your middle or index finger on the 19th fret is to put 24 on there and guilt out the designer. It does get kind of gimmicky, though - short lengths of string don't really sound very good to most people.
*(torpedoroni, don't ask)