Benefits and drawbacks of Dropper posts?
There are generally two types of dropper seatposts, mechanical (e.g. GravityDropper) and hydraulic (e.g. RockShox Reverb). Mechanical dropper seatposts use a spring to move the seatpost and a bolt to keep it in place. This is a very simple design and there are few things that can break or jam, and the weight is also kept very reasonable since there are few parts needed to make it work. The drawbacks are that you only have a fixed number of height settings, i.e. fully extended, halfway extended, and fully lowered. This is because the seatpost is being held in place by a pin that goes through a hole in the seatpost.

A hydraulic seatpost on the other hand uses hydraulics to move the seatpost and thus allows you to place the seatpost at any height you like. The drawbacks are that they are more complicated, usually weigh more, costs a lot more and requires more maintenance. The advantages are the ability to lock the post at any height you like.

Mechanical dropper posts:

 + Mechanically simple and easy to maintain
 + Low weight
 + Cheap
 - Only a fixed number of positions for height adjustment


Hydraulic dropper posts:

+ Freely adjustable to any height
- Complicated
- Requires more maintenance
- Expensive


Static QR seat posts:

+ Requires no maintenance
+ Cheap
+ Low weight
+ Can be adjusted to any height
- Rider must dismount to lower and raise seat