How "being on a diet" on indulging emotions is different than invalidating feelings that could be useful information?

About indulging emotions, I don’t get how they are not useful to us like any other negative emotion would be? I mean, being angry toward something makes me realize that my boundaries were not respected, and it makes me act so they are respected in the future, or walk if it happens again and again.

How is it different with, for example, worry? To me, worry makes me point out something that requires my attention and needs to be monitored. For example, I’m worried my BF is working too much, I don’t have any control over this, but I can still point out my worry to him, and talk about it.

If I just “got on a diet” on that worry, then I feel it’s not being managed at all and could easily come back again and again until the circumstance evolves. And how is that “diet” not a way to just invalidate feelings?

I’m still new to scholars and I see there’s something I’m missing. How am I not thinking straight about all this?