This would be very nice if you're betting unders on an over/under.
It would also be nice if you're betting on an underdog to cover a spread. There are occasionally basketball games where a team ends up winning by double digits in overtime. And teams win by 7 points all the time in CFB overtime and 6 points in NFL overtime. There's even been one 13 point overtime game in CFB-USC vs Arizona State 1996. Under the new NFL overtime rules, it's theoretically possible for a team to win by 9 in overtime (if the first team to get the ball gets a FG and the opponent throws a pick six on the next possession), although I've never heard of it happening.
Anyway, even leaving aside the 13 and 9 point win longshots, there's hardly anything worse than betting for a 6.5 point underdog and losing because they lose in OT by 7.