I just got the terrifying presence perk, and im thinking about loading and getting something else..

I was wondering if its useful?
or could anyone give me an example of what happened when they used it

Nope. At least in my opinion its useless.

I do not think one situation has come up where I would need or even want to use that perk.

Just load.

What about the concentrated fire perk, how exactly does that work? Does the accuracy go back down when you leave vats or when your out of combat?

I haven't seen many opportunities to use it on people other than those that the developers already figured you may have to become enemies with, so there really isn't a point to it except as a way to start combat with words instead of weapons, even though you'll just use weapons after using it anyway. You can't just go up to a trader or a random wastelander and go "Growl I'm intimidating," it has to be certain people, which really defeats the whole purpose of it. The only time I've ever seen it as an option was when interviewing the captured Legion soldier at McCarran, and even then using it would have been the opposite of what I wanted to do. Keep in mind that I have a really high speech stat so it isn't like that could be stopping the option from appearing.