This is true.
We over plant beans because we assume some won't emerge, some will get damaged as they grow, hail maybe, and so forth. Beans try hard to adjust their growth for the crowding or lack of crowding they face during the year. Most of their seed production depends upon the moisture and conditions in September; before that is just growing branches and vegetation to fit the crowding or lack of crowding in their world.
An issue with thin bean populations is weeds - weeds are gonna be a lot worse in a thin bean stand, you really need to stay on top of the weeds if you have a thin stand. The ground will be much more open much longer as the beans take longer to fill in the canopy, and weeds will take advantage of -every- rain to grow through those bare spots long into summer!
A good issue with thin bean population is white mold - the more air can circulate down under the canopy the less white mold you will get, if that is a concern in your area.