My views on jump jets have gradually evolved from "waste of tonnage that could be used for more Clan pulse lasers" to "situationally useful but not essential" to "nearly required for almost everything" to "why doesn't it have IMPROVED jump jets?". So, as far as I'm concerned, the more broken the terrain is, the better. That, and I've recently been playing a lot of games that pit high tech, high skills, and small numbers against decent tech, less skills, and 2:1 odds. So, anything that allows me to break line of sight and keep the opponent from focusing everything on one or two units is a boon.
That's just me looking for an advantage, though. I could certainly see how no jets and average pilots could make a map with a lot of trees and hills take an absolute eternity.