Dropping the seat height will improve the bike's stability and handling during cornering and braking and guarantees shorter braking distances. The lowered CoG when you dropped seat does that and improving handling by lowering CoG is one of the basic concepts in vehicle dynamics. A better handling bike is a safer bike so it's not entirely a waste on a road bike even if you never intend to use it as dismount aid.
I don't use dropper post on my road bike but I do adjust the seatpost and drop the seat before going down a long downhill. I've seen enough silly videos of roadies falling flat on the pavement during a fast descent because they're unable to brake for anything because the high seat would make them tumble over or lose control of the bike.
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I would have equipped my road bike with dropper post but my road bike is not compatible with dropper post.