IMO, QT should only be used in two cases:
(1) Where you suspect that your newly acquired nem is sick and that treatment will likely be necessary.
(2) Where you already have healthy anemone(s) in the DT of the same or similar species as the newly acquired nem. In that case, you QT the new addition to prevent spreading the pathogen to the existing nems.
Other than these two scenarios, I am a firm beleiver that a QT will only do more harm than good because they can never be a true substitute for a healthy established DT.