Sidemount diving offers many advantages over the use of traditional back mounted cylinders. In the past, options for increasing gas supply available for a dive involved manifolding two cylinders together, which doubled the weight a diver had to carry on their back.
With sidemount diving, the cylinders move from your back to your side. Transportation of cylinders topside is then much easier. Cylinders may be donned after entering the water, eliminating problems with wearing heavy cylinders out of the water. Redundant gas supply increases bottom time, and adds an extra level of safety to the dive. Sidemount diving provides added stability with the cylinders on the side of the body and double the gas supply. It is an alternative way to streamline in the water, easier to “trim out”, and the diver has the ability to monitor all their equipment because it’s right in front of you.