Definitely have a dropper on my mountain bike for riding bumps and drops, it is essential. I like it so much I installed one on my Specialized Allez road bike a few years ago and enjoy the fine height tuning on long rides.

I just bought a Trek FX Sport 4 for road riding and I am replacing components to make it really lightweight. I went with a carbon fiber bars and seat post to save weight.
Those dropper posts are heavy. Mountain bike guys are not as weight sensitive since they are always going downhill.