that's true. On fenders you can have the smallest damage but if it appears that it's rolled or damaged in any way by the bumper it's instantly replaced in good shops. Doesn't mean the tech can't fix it, just means the shop doesn't want to gamble on it cause you wear out the tabs mocking it up when you work it.
So basically, you can have that side of the bumper hanging while you work it and mock up. Of course after you get the bulk of the damage and get it looking like the other side. Look at the area that hangs over the bumper. That will tell you a lot about where it needs to go. If you don't deal with this issue martin speaks of then you might have a corner of the bumper in or out or not a great fit in general.