Efficiency is the name of the game with all power use.  If you can call down the wrath of God once and then have to go smooch your partner for half an hour, you're not going to be much of an esper.  You need to be able to work all day, or at least all dungeon.

"Okay.  Remember, I'm not going to buff you long.  Just enough to get this chunk of rubble out of the way.  If there's anything wrong, you tell me.  If it starts to break, you tell me.  If you get a bad feeling, I want to know about it!  We've gotta do this stuff all day, people.  I don't want to cut out early because I had to save you from getting crushed!"

It's late in the evening on the first day of Arrakis.  Sara'd been whisked away to wherever precious sensors are.  Not that he's bitter - he's a sensor, but he's really not suited to the job of finding people in rubble.  What he can do is fit ten men's worth of strength in a four-man package.  Well, three women and a man, today.  And Griggs, but his job is to observe 'till there's a victim, then spirit the victim away.  But in a good way.