Being shot by a phaser set to disintegrate/vaporize is rather a tidy death:
since when hit in the clothed chest, the shirt, pants, shoes, and entire lifeform within all disappear (so Kirk has to rely upon his rakish charm rather than simply shooting the clothing off nubile aliens).
But the disintegration doesn't propagate through the shoes into the deck - perhaps that's too big? What if the victim was sitting in a chair with his feet off the ground - would the chair disappear too? If they're shaking hands is the shakee going to go too? How about penetrative sexual intercourse - does the penetrator "wear" the penetrated? The countless bacteria in the gut certainly vanish (much to the relief of Starfleet janitors)
Presumably along with all the other safety instructions and directives to wash hands after visiting the powder room, new Starfleet inductees get briefed on the nuances of vaporising malefactors - what are these rules?
(the dull out-of-universe explanation seems easy: dissolving between before and after views with a little rotoscoping is a lot easier than a convincing suddenly-empty-clothes-drop-to-deck effect. But it wouldn't be Star Trek without a loving in-universe rationalisation)