Ich is the least of diseases I quarrantine against, at least it is easily treatable. Even when you can identify a disease or parasite it can be difficult to safely treat & without killing otherwise healthy fish, plants & inverts. Q= safer, easier, cheaper.
I will admit to a shortened Q period of only 2 weeks once in a long while instead of the usual 4 weeks or more. Sometimes I'm unable to resist a new find or an emergency crops up.