I've used them in terms of Warmachine "Hardcore" play, which has very strict turn time limits. It's an interesting format, and it actually changes the meta-game. Not something that I think is really suited to a friendly wargame, except for situational examples where it's particularly thematic. Space Hulk had a turn time limit, and it was extended based on the number of terminator sergeants or captains present in the mission. I liked it there for the atmosphere it added to the game, but Space Hulk is quite a bit simpler than Legions of Steel or Planetstorm. Moreover, I know tons of people who never actually used it in Space Hulk, even though it wasn't an optional rule.