I think if you have a double blowout week, disabling garbage time in at least 1 game makes managing game shape way less of a pain in the neck (especially if you're out of the cup).
Also, disabling garbage time in the first half of the season makes it easier to farm all star votes, which seem to be based on some combination of rating and minutes played at a position based on my limited observations.
Personally, I've always had very good GS with ~72 minutes, a massage doc, and a sports psychologist, so I plan to always disable garbage time. Will make it pretty easy to get 60-72 minutes across my team with an 11 man roster once I drop out of the cup.