If a team has questionable DBs does it ever make sense to blitz, or is it best to keep as many back in coverage as possible?

It seems to me that an occasional blitz might help to minimize the chance of the opposition having a long, time-consuming drive. I guess this "bend but don't break" approach shortens the game which reduces the opportunities for the other team to score, but it also makes it likely like you'll lose the TOP battle and have a tired defense. Wouldn't at least occasional blitzes at unanticipated times make sense to the opponent guessing and to keep them from getting in a groove offensively?

If a team has good DBs it seems that a team could leave them in man coverage more often and run more blitzes to keep the opposing QB off-balance, and to increase the opportunity for negative yardage plays.

Bottom line, I may be wrong, but it seems like Tuiaki's approach stays the same regardless of the quality of BYU's DBs. There are typically no surprises, opposing teams consistently get long drives, the game is shortened, and it's generally a low-scoring game. This makes it more likely that BYU will have close games against both good and bad opponents, regardless of how good the BYU offense is.

What am I missing? Is blitzing really a high-risk/low-reward defensive approach? Seems to me that consistently dropping 8 is a low-risk/low reward approach, and often helps the opposing offense get in sync and put together some long drives that end up tilting TOP in their favor, giving them an increased possibility of winning the game.

What is the truth/reality?