YES, it's a very good thing to do if you want the most and best sequence possible. We load based on the largest fragment in the group, so if the size spread is wide you'll get fewer clusters/sequences. Cluster detection is more accurate when all clusters are the same size (wide range of fragment sizes results in wide range of cluster sizes). Additionally, very large fragments don't stay denatured as long and will often just roll through the flowcell or even interfere with the annealing of the smaller fragments.