
Here we see the wide receiver and the second tight end streak deep. The first tight end and the running back both bolt for opposite sides, and the third tight end takes his defender (likely a cornerback) towards the center of the field. If the defense is in zone, they have to hope that every zone is covered. This is not likely, since the offense will have been pounding the ball with a goal line looking formation for several plays.
But what if the defense goes to man coverage?
How about the run game plays? Let's take another look at the base three tight end formation.
In the above diagram, the first tight end can line up behind the right guard, behind and centered to the right guard/right tackle, or behind the right tackle. The third tight end can motion to any of the spots just mentioned. As the offensive line zone blocks with a rightward slant, the tight ends nearest the line join the zone, while tight ends behind the line look for opponents to take out (much like a fullback would).
[...]
There are more potential formation combinations that proceed from motions in a three tight end formation than any other formation in football. Because of the dual role of the tight end position, the formations become more difficult to adjust to. Here's a simple example. Looking at the above diagram, picture the first tight end motioning to the right sideline before the play. Question: Does the defense
1. Take the cornerback on the third tight end out to cover the first tight end, while switching the middle linebacker to one of the remaining tight ends (leaving the strong side linebacker to figure out his coverage), or
2. Have the middle linebacker follow his man all the way to the edge of the field, leaving the middle of the formation exposed to a run?
https://footballtimes.org/three-tight-ends-offensive-formation/