An underdog should adopt high-risk strategies. Usually they won't work out, and instead of losing by 7 you end up losing by 20. But that approach increases the chances of pulling out an unlikely win: it expands the range of possible outcomes. Variance is the underdog's friend.
When you're the better team, you want to minimize variance. You're better than they are: as long as weird stuff doesn't happen, you'll win. So you want to reduce the chances that weird stuff happens.
What you don't want to do, though, is slow the game down. On average, you'll score more points per drive than they will. So the more drives there are, the more that advantage builds up. If you slow things down and reduce the number of chances to build up that scoring advantage, you let them hang around and give them a chance to beat you with just one or two wacky things happening.
So, against a much weaker opponent, play fast but not risky.
Against a stronger opponent, play slow and risky.
