Well, dropper posts were originally for off roaders that do a lot of technical terrain where they don't want their saddle to interfere with the control of the bike when it's bumping all around.
Where it helps me is whenever I have to stop - at intersections, stop lights, traffic, etc. At my normal saddle height, my foot is about 4 inches off the ground which forces me to get out of the saddle to stand with the bike. Now, all I have to do is trigger the lever and my saddle drops down with me on it so that I can put my foot down without getting off. It's one less thing to manage as traffic begins to move again and I can jump with the the traffic flow right away. I just pop the seat back up when I want to get going. I usually stand on the pedal when I'm ready to go, hit the trigger to pop the seat, then kick the throttle. It's super quick now.
The other thing, too, is that the stock saddle is really grippy, so sliding on and off it is not very easy. It always grabs my shorts, ...that sounded weird...
The PNW Cascade post also has air suspension, so it takes up some road shock from the hard tail. It's pretty subtle, but effective.
