The Sidemount Diving configuration began in cave-diving, and has evolved to be suitable for recreational open water diving. There are 5 key benefits: With a proper side mount configuration a diver can transport two much smaller cylinders to the water before gearing up, reducing the weight of scuba gear on the surface and during entry and exit points. You have two independent air sources for redundancies underwater. You have increased ability to move weight (cylinders) for proper trim. You are more streamlined underwater. Finally, you have an increased ability to access gear underwater (for gas shutdown etc).