Seromas accumulate in what is known as "dead space" where a potential place for the fluid exists. Efforts are directed at reducing or eliminating the dead space.
Quilting sutures reduce the risk of the skin–fat layer's separating from the deeper muscle layer, and having the separation fill up with fluid, by physically holding those layers together. Drains suck the two layers together so the body's natural "glue" (fibrin) and wound healing have a chance for a permanent bond.