Flying from right seat of Socata TB9 - confused about Pilot manual limitation (US regulations)
Most airplanes are designed for the pilot to be in the left hand position, so some have controls on the left side that are inaccessible (or very hard to reach) in the right hand position, like parking brakes, fuel tank selectors, nosewheel tillers (on big jets), sometimes the key is hard to reach. On the TB9 the circuit breaker panel is by the LH pilot's leg, it would be extremely challenging for someone in the RH seat to reach those, and they could be important if one blows in flight or there's a fire. 

The important things is that the person in the left seat is capable of and has been briefed on how to operate any controls required during the flight. 

Personally I don't see why you need to let people sit in the left seat to give them a taste of flying, the right seat is just as good for that and it is less risky.