Holding on to anger is not really any different than grabbing a nail-studded potato. It hurts, and ultimately doesn’t accomplish anything.
Unless, of course, you can use that anger against the person who has wronged you. For instance, by hurling a nail-studded potato at them.
Repeatedly, if you like.
Sure, forgiveness is nice, and ultimately, you should probably aim for that (or at the least, learning whatever lessons can be learned and moving on).
Until you’re ready to move on, though, aim for the soft, squishy parts. More chance the nail-studded potato will stick that way.