Scap wall slides are great for the overhead athlete to activate the serratus anterior, a big time muscle for the overhead / throwing athlete. The serratus is an overlooked muscle in the grand scheme of shoulder function, but it might be on the of the most important for throwing athletes. Right now, we're perfomring scap wall slides as an activation warmup series prior to all our upper body work. We usually focus on 2-3 sets of 5 reps with controlled movement and pauses at both ends.
Check out some of these previous posts for more info on the serratus and the scapular function and how to tie more serratus work into your training.