It is a matter of deciding what is important. I just spent $540 U.S. on DNA tests for the blue egg gene on 9 roosters and 9 hens. The feather samples are being shipped to Justus Liebig university in Germany. If I test for the gene, I can eliminate the cost of raising a dozen hens from each test rooster in order to prove which roosters are homozygous for the blue egg gene.
Doing it the hard way, I would have to raise chicks from at least 8 roosters to find one or two roosters that are homozygous. That means I have to raise 96 hens which means hatching at least 200 chicks (both male and female). Each hen I raise costs me about $30 which means I would tie up roughly $3000 indexing roosters. By comparison, I can do a DNA test on 8 roosters for $240. I rather fancy saving myself $2760.
For similar reasons, using DNA tests to identify a couple of homozygous rose comb roosters would save quite a bit of breeding and selecting. Feed gets expensive if you raise a few hundred chicks.
One thing I should have mentioned is that since rose comb is caused by a chromosome inversion, it is always a possibility that the inversion could revert to normal which would result in straight comb birds. This is extremely improbable, but even low probability changes can still happen. After all, the rose comb inversion is present today because it occurred on at least one occasion sometime in the past.
