For reasons discussed in the replies here, I think everyone should try mtb riding. There are a lot of skills learned via mtb riding that would help a roadie, inc how to generate power in an efficient manner. Too much and you spin out and end up walking the bike, too little and you don't make a climb and walk the bike..... while those in your group ride up. Then there is getting over/around obstacles.... and so much more.
For me, power can come from either position but typically while standing on the bike, but that doesn't last for very long and takes a lot out of you.