Max protection is used If a QB is reading an overload on one side of the ball, then he can kill a route to have the TE stay in and help with the extra man. He can also move a player to help with that.
This protection may have two running backs or, a FB and a RB to bracket the QB. It can use two tight ends, one to block and one to run a route, there a few combinations all based on what the defense is doing.
The drawback means only 3 players go out for a passing route, which can limit the choices the QB has to throw to. However, depending on the personnel, it can trick defenses. Blake Bortles has thrown a touchdown to a FB from this protection.
Besides using this grouping to protect the quarterback, it also can help block for a run. No matter the reason, whether a designed play or not, the QB can change an assignment (as in, change a TE from running a route to blocking, etc) or he can move the RB from one side or the other – those are just two examples.
When a defense loads up one side of the offense with pass rushers or blitzers with more defenders than offensive lineman, the OL can shift their call to the protection. Which is one reason why you may hear the Center and/or QB yelling “#52 is the Mike”. That is centering up the defense from an offensive perspective so they can apply their rules/calls.
Sometimes an OL is weak because they’re not good or a back-up is used due to injury and Max Protect has to be used more than desired. If that’s the case, the offensive coordinator better be creative because defenses can use the extra DB to harass.