Triple T said:
You're in high school bud, that comment doesn't really apply to you. (And considering the fact that we're in the high school form, I feel silly, but regardless what I say holds truth.)
You should make friends with everyone in high school because you're forced to socialize. And there is no harm in widening your social circle either, don't take it that way.
In college and then out of college, you're responsible for the company you keep and there is a much larger selection. When you're past 21+ you're normally only interested in her for one thing and not really her outside life. This includes her friends. When you interact with her friends, you run the risk of being c0ckblocked at some level. Especially if the girl you're going after is more attractive than her friends. If you're at a bar, one of her friends may "accidentally" drink too much, or want to leave, or be an outright b1tch.
Or you may find out her friends are much hotter than her....
Sure, making a good impression on her friends isn't negative, and if you're looking for a girlfriend it can't hurt. But you shouldn't make it a habit of commingling with her friends, it can complicate things.