When is it OK to crowd the pan?

I am reading some books on cooking technique and often see the guidance "don't crowd the pan" when sautéing or pan frying, so that food cooks by browning/maillard, rather than steaming. However, many recipes I find online and in cookbooks involve piling many ingredients into one pan.

A couple of recent examples from NYT's Mark Bittman:

http://ift.tt/1ySAV98 (onions and mushrooms) http://ift.tt/1ImQ4Jt (onions, bacon, mushrooms, chicken, garlic) http://ift.tt/1ySAV9a (onions, carrots, celery)

Are these exceptions to the pan-crowding rule? Or is it just that it a matter of convenience to put everything in 1 pan?