Of Mice and Men why does George ask Lennie to familiarise himself with the location of the clearing?
I, too, believe that this is George's way of protecting Lennie with a place to hide if or when he gets into trouble again. George knows that Lennie does not do well with thinking for himself especially when he is under stress as he is when he is in trouble. Therefore, George teaches Lennie that he can just run to the prepared hiding place, and George will find him there. It gives Lennie and George a specific place to meet if they need to find each other in an emergency or when Lennie needs to leave suddenly again.
George is anticipating trouble. He realizes that Lennie can find himself in trouble easily. He is preparing for such an instance. If he and Lennie should have to make an escape, George is preparing Lennie for a place that they can meet. George is used to Lennie getting in trouble. He is used to having to make an emergency run for safety. Ironically, Lennie does get in trouble and he has to run for safety at the clearing. George knew where to find Lennie. Of course, this would be Lennie's last run.
As has been pointed out above, George can't quite trust Lennie to stay out of trouble. They have to have an escape plan because of the likelihood of needing to make an escape.
This is a sad and telling hint at Lennie's ability to enact self-control and at George's dilemma - in taking care of Lennie, George has to put other people at risk. He chooses to protect Lennie, to side with Lennie, and goes so far as to create an escape plan for Lennie's next (violent) mistake.
I believe it is so that Lennie can come back there if there is an emergency. George knows that Lennie has a tendency to get himself in trouble like he did in Weed. So maybe he thinks that there might be a need for Lennie to get away to somewhere that is secluded and where George can find him.
George tells Lennie to remember where they are as an escape plan. They seem to have required something similar before - this is probably how they came to hide in the irrigation ditch when they were run out of Weed.