If you already have fish in your tank that were never properly QT, there is no point doing it now.
What you are talking about is more of an observation phase, where you get the fish and make sure he is eating. But I personally think that its more stressful the fish to be move around multiple times than to just put them right in and you should never buy a fish that inst eating at the store (make sure you actually see them doing so).
The only time I think an observation phase would be useful is if you have a very rare or fickle fish and they need time to recover from shipping, need to adjust to the tank and feeding. But as a new reefer you shouldnt be purchasing those fish in the first place.
If you do have sickness, moving the fish can cause enough stress for them to die, and often times the disease will still be in the main tank just waiting for another moment of stress to come back. And if you do end up treating, most of the meds will wipe out the bacteria population and you are going to need to do daily water changes anyways.