I might be wrong, but when I use them I drain and rinse if using canned, and then measure them out and add to the counter accordingly. The easiest is to cook beans from scratch (which is really easy and eliminates any guess work), but that can be difficult at times, especially if it's an impromptu meal.
The biggest thing about the canned beans, I think, is the sodium. If you're draining and rinsing them, you're eliminating most, but not all, of the sodium. That's why I prefer the cooked from scratch method.