I think it depends on the breed.
My cavalier king charles spaniel rarely needs a bath, his white stays pretty white and his black is very shiny. He gets a bath about every 3 months or so when I take him from a trim.
My standard poodle, on the other hand, gets a bath about once a month. He is like a living Swiffer, everything sticks to him and stains his coat! We do agility and the place where we train has a black rubber mat floor that stains his coat and for some reason smells awful.
It really depends on your dog. Bathing too often will definitely dry out the haircoat, especially if you don't rinse rinse rinse and rinse some more.

In a pinch I use a 'dry shampoo' on Flip, to get stains out, etc. When he was a smaller pup he used to pee on his front legs once in a while.

That is where I learned about the spray stuff. It works pretty well. This is it:
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