Explain this penalty to me.

I think it falls into the category of rules that helps defenses set up or make adjustments. Kinda like the 12th man in the huddle rule or that rule we heard during the Eagles game that in a hurry up offense the defense has the right to adjust if the offense makes a substitution. I can kinda understand the rule. If that rule wasn't there offenses would be lining up in illegal formations, confusing the defense, and then hurrying up to get into a legal one and snap the ball.