Imagine this scenario, which happens often enough in an NFL game:
Team A losing by 3. 2nd and goal at the B10. Chip shot field goal range. Team A has 1 time out.
:08 left 4th quarter
Team A has enough time for 2 plays. One more attempt to score a touchdown before settling for a sure field goal if they don't score the TD.
During this 'free play' by Team A, why doesn't Team B just hold and tackle every Team A player? The idea is to eat the seconds on the clock, so Team A's only option is to kick the field goal to tie. Team B doesn't want to give Team A the opportunity to win the game. No matter what the foul is, even pass-interference in the end zone, there would be say :02 left. Team A most likely will settle for the field goal to tie as now there is just 1 play left.
Team B could also intentionally jump the snap to beat a blocker to force the QB to throw early. Or use both techniques.
The basic idea is to run the clock down from the offense having 2 plays - to just having 1 play.