Depends to where the fish are coming from - for example a LFS on the same water supply you probably don't need to acclimate. However, if your LFS runs on tap and your tank runs on RO there could be a much bigger difference. One of the benefits of a quarantine tank is that you can set it up to match the water they are coming from, temperature acclimate and then plop them in, then do the acclimation over a few weeks until it matches your display tank. The you get best of both techniques and minimise disease risk as a bonus.