Mr. Fishy runs small groups so he started making henchmen. Party hires a henchmen to follow them around and soak attacks and help with puzzles, like standing on a plate or pulling a lever. Working out the puzzle is still PC work.
Mr. Fishy has played in games with GMPC's who were handled poorly.
But Mr. Fishy has seen them handled well to and it can improve the game by giving the players a connect to the world they might no have otherwise.
However, the NPC has to be handled carefully or he become a Gandalf figure. A GM device to save the party from an overwhelming encounter, rather than a tool to help the party. Mr. Fishy prefers to let the party decide if they need help. Mr. Fishy will add a NPC for limited run if that NPC is a story character.