First rappeller to the ground: untie stopper knots
Does your rappel end on the ground? Do you have plenty of extra rope lying in the dirt?
Here's a quick task for first person down: Consider untying the stopper knots in the rope.
Once you’re on flat ground (unless the previous rappel was a real rope stretcher, and you barely made it) stopper knots are no longer needed.
If the first person unties them as a (mostly) regular habit, it eliminates the possible BIG problem of pulling a knot up out of reach when you pull your rope.
If this hasn't yet happened to you, it likely will someday, and it can be a gigantic hassle. Simple solution for a common problem!
If untying your stopper knots makes you nervous, here's an alternative. Untie the stopper knots in each strand, and then tie the ends together with a simple overhand. Now, you still have a closed rope system, and your partner coming down can’t rap off the ends. But you also have a loop of rope, so you can’t absentmindedly pull one end up out of reach.
If your rope barely makes it to the ground, this might be the best of both worlds.
There are very few “always” and “never” rules in climbing. This isn't one of them.
There are some cases when you want to leave the stopper knots in, such as:
If the rappel is a real rope-stretcher, and there's very little rope on the ground.
If the rappel ends on some kind of a downward slope. There’s a chance your partner above could swing from where you landed upslope to farther downslope, and potentially rap off the ends of the rope.
A double rope rap with ropes of say 7 and 10 mm, and for some reason, you tied the joining knot on the fat side instead of the skinny side, there's a chance your rope ends can “migrate” because of the extra friction from the larger rope.
For the vast majority of standard rappelling scenarios, if you've got a decent bit of extra rope on flat ground, untying the knots like this is going to be just fine.