This way when you choose clerkships you will be picking programs you know you are competitive for, offer decent training, etc. If you have free time I would also visit possible programs you may be interested in clerking at before you make final choices. Some students may argue that the point of clerkships is to get to know the program but I've seen plenty of students clerk at programs they had no business clerking at (its not that hard to clerkship months a top programs) only to be denied an interview when CRIPs come. You are investing time, money and stress towards trying to match into the programs you are clerking at. Make sure you know they will count.