When connecting stranded wiring (a wire that is made up of numerous smaller wires as opposed to a solid wire) all strands of the wire must be secured under the terminal screw.
In this photo of a wire connected to a circuit breaker, there is less wire connected to one of the connections which means more load going through a wire that’s half the intended size.
As electrical load or draw increases the connected wire strands will be forced to move more electricity than they are able to handle. This will cause the wire to over heat, eventually scorching the plastic insulation and possibly causing a fire without necessarily tripping the circuit breaker.
This poses a serious fire hazard and is very poor workmanship.