In helicopters, the normal seat is the RHS, so the pilot can still control the cyclic with right hand and operate the centre console stuff like radios, GPS etc with left hand. Instructors in the LHS have to learn to change hands and fly left-handed to use the right hand on radios etc. which can be a real fiddle.
Most helicopters will specify the solo seat to be the RHS, but many long-liner machines have the LHS set up for flight from that side, moving throttle quadrants and placing spare torquemeters etc into the line of sight.
An instructor on a solo flight will follow the flight manual, and drive from RHS. For instructor training, though, there might be a "sandbag" in the RHS while the new instructor scares himself from the LHS for practice.