Side Mount diving has been around for decades. It was originally designed to explore cave systems that required long treks underground to sumps. This necessitated the need to break the kit down to smaller and more easily handled components for entering and exiting the water, diving, and moving through dry passages.
Sometimes the best dive plan dive runs into a detour, it shouldn’t happen but occasionally it will. The intention was to do drift dive along the reef with your dive group. However, that yellow frog fish caught the attention of you and your dive buddy and now that group is out of site.