Rowing with no foot straps can help you engage your core, maximize the leg drive (as you have to press down on the feet cups) allow you to have a better...
Amazon.com : Foot Straps for Rower Compatible with Concept 2 Rowing Machine Model E and D Rowers(1 Pair) : Sports & Outdoors
Footstraps for Concept2 Model D-E-Dynamic Indoor Rower