There is a lot that can be said about this. I have never played line or coached the line, but have been around the game a lot as a player and coach. When there is a running play, typically it is either man blocked or zone blocked. It is important that the blockers recognize whether the defensive front is in an odd front (usually 3-4), even front (usually 4-3), or something weird like a short yardage/goal line type front. These fronts determine how the blockers will go about blocking the play. For example, you don't want both your guards blocking two defensive tackles when the defense is in a 3-4 and there is only a Nose tackle. The center will determine which front the defense is playing and the blockers adjust accordingly. On a given running play, the offensive tackle may be responsible for the end in an even front, the LB in an odd front, or the Defensive tackle in a goal line front.
I am less knowledgeable in pass protection issues, but usually the defense tries to determine who is playing middle linebacker. This helps them determine if the defense is overloading one side and if so they need to slide the protection that way, or have a running back pick someone on that side up.