What types of transactions may require reversing entries?

An examination of the ledger shos this error: The Service Revenue account was totaled at $5200 instead of $5280. How do I correct this on a T-account? Do I just add the 80 bucks or is there something else I can do, none of the research I have done has been able to help neither does my book!!

I know reversing entries are used to keep from confusing and over/under estimating a certain account in the next period, but here's my question. Are reversing entries really necessary in your accounting period?; even though they are meant for reminders there are other ways of doing that without...