It can grow to the point that there's no more room for it to grow. I don't think it can hurt the system but keep in mind that the whole point in having it is for nutrient export. Unless your macro is able to grow it doesn't use up excess nutrients.
It's fine. This type is pretty safe. It's very invasive & you don't want it in your display tank but it doesn't do the reproductive thing as often as grape & a few of the others. Keep it trimmed & growing and it will do well for you. If you noitice it turning white take that part out. As far as ID I think it is:
Fast growing macro-algae.