DF,
While new barrels are usually pretty clean when new, most still have the remnants of proof or test-firing in the bore, so need to be cleaned before installing DBC. In fact, the bores of the unnamed rifle brand known for barrels that foul considerably often have enough copper in 'em to be very visible at the muzzle, just from test-firing a round at the factory.
Aside from instances like that, I give 'em all a chance to prove whether they're going to foul or not before installing DBC. We own one very accurate .223 that has gone 500+ rounds without cleaning, with no deterioration in accuracy, and has never been DBC'd. Have several other rifles that will go around 200 rounds without cleaning, and don't bother cleaning them either.
But then, aside from when installing DBC my normal cleaning routine is to run a loose patch soaked in Montana Extreme through the bore, wait overnight, then push a couple fresh, tight patches through.
