This approach to band pull-aparts involves doing isometric holds in various positions. This is great to improve muscle control and transfers well to the bench press where the back muscles must work isometrically to create a strong base to push off from.
Those guys who think planks and Bosu Ball triceps kickbacks are giving their core a good workout are poor, pathetic slobs. If you really want to work the core, you've got to raise the weight over your head.