You can trim it (not all the way back) I don't think it crowds too bad but it depends on what plants your worried about. And also it looks WAY different after flower don't worry it will fluff up the following spring and flower again.

It crowds like CRAZY. It grew up, inside and over the outside of a pine bush for me last year. It didn't kill it, but boy that felt aggressive for me. It's not terrible to cut back, but honestly a find a sharp shovel to be way easier. I just dig it. That way I get a nice clear edge line. I pretty much do this every spring or I fall behind and regret it. That being said, once a year with a shovel isn't too bad.
I like the look both green and flowering.

More green.

Ah, thanks for that! I guess I will confine it to areas near shrubs and keep it away from the perennials until I am more certain about it. Thank-you.