It is not usually recommended to routinely treat all quarantined fish with copper. Copper is moderately toxic to fish and can increase the amount of stress that they are under. Some people routinely do hyposalinity on all their new additions as this may even lower the stress a fish is under. The purpose of quarantining is to allow any hidden parasites to show up as they complete their lifecycle. If you are buying from a reputable source the fish will merely be watched and then they can go into your display after three weeks. This also forces you to add stock slowly to a young fish tank.
I used to wonder about the value of having a QT myself. I never did this when I kept freshwater fish. However, consider how you would feel if you lost several, if not all, of your expensive fish from a preventable disease. Also consider that it can be nearly impossible to catch a fish without dismantling all of your live rock. Also consider that there are no medications that are recommended to be used in a display tank (and that many are toxic to live rock, inverts and corals).
After experiencing a case of ich when I was starting out and losing 6 of my 8 fish, I now think that it is utter foolishness NOT to have a quarantine tank.
