I suppose I get the reasoning behind it in a way. In terms of- if you can't forgive (or forget) something, it can go on hurting you over and over. So, for our own sake, maybe it's healthier if we are able to let things go. Easier said than done of course.
What I think is more relevant here is trust though. When someone wrongs me, it changes my opinion of them. I'm much more wary of them and some of the trust I had in them goes. That can be minor. As in- they may often make plans or offer to help with something and then cancel- they're unreliable. So- to protect myself, I try not to rely on them in future. If we happen to plan to do something again, I don't set my hopes on it happening.
Or- it can be something major. Enough happened with someone in my childhood for me to believe they are a narcissist. I will try to avoid them at all costs because in my opinion, they are incredibly toxic.
I have thought about this in the past though. Have I forgiven them? I don't feel like I exactly hold a grudge as it were. That's just them in a way- to my view. Maybe they can't help being the way they are any more than I can help being me. That doesn't however change the fact that I believe them to be a very harmful person to be around- so- I wouldn't be, if I could possibly help it.
I also feel like forgiveness is the most relevant when you want or need to continue to have a relationship with the person. Seeing as I never want to see this person again- it doesn't affect any relationship dynamic. It isn't even relevant to them whether I forgive them or not. It isn't massively relevant to me either because, I don't have anything to do with them.
I guess I suppose it depends doesn't it? I suppose forgiveness is saying something is now ok. It's not saying the thing that happened wasn't bad and it's maybe not saying the person who did it wasn't at fault. But, I guess it is saying- I'm going to put it behind us. Maybe we shouldn't be saying it if we don't mean it and, depending on what it is, maybe not all people deserve a second chance. Plus, if they keep doing the same thing over and over, then- they're clearly not sorry!