I have mixed feelings, for most things I suspect QT is more stressful on the fish then the QT med.'s or hypo is good for them. I lost a tang that was eating and looking ok and was 2 years old but he had ich. My other fish were stressing him out so a freind agreed to take him after the ich was gone. I Qt'd him and did a hypo treatment for a few weeks, the fish was stressed out the whole time and towards the end he stopped eating. The last day of QT and we were going to take him to our friends tank I came home from work to a dead fish
On the other hand if I had started QT earlier (or QT'd new fish in the first place) when I went through the marine velevt I most likely would of been able to save most of my fish. Instead I left it too long (because I didn't like QT) and had most of my fish die.