IMO, as you start thinking about more difficult or expensive fish, a dual QT setup starts to make sense. I run both an 'introduction' tank and a 'hospital' tank. The former is setup permanently as a full, albeit small (30 long), reef tank with LED Par38 lighting, a small skimmer, a small UV and live rock. All inverts go into this tank as do all new fish. Generally invert 'treatments' are dips so that can be done relatively easily. If a fish requires treatment, I move it into the 'hospital' tank which is only setup as needed. I keep a few bags of those ceramic bio-rings in my main sump to use as required.
1. With sensitive fish, I try to get them acclimated and eating in the 'introduction' tank before attempting any kind of treatment
2. I don't medicate prophylactically, only as symptoms become apparent
3. Although no medications are used in the 'introduction' tank, if a fish get sick and needs to be treated, the tank then stays fishless for 12 weeks.
4. Symptom-less fish remain in the 'introduction' tank for at least 12 weeks.
5. I use an acclimation box when moving them into the DT
This approach has really worked well for me and since doing it this way I have successfully moved 9 fish into my DT with only a single loss (stupidity on my part though, as a Bartlett Anthias went carpet surfing out of the 'introduction' tank). Fish successes include a Potters Angel, a Purple Tang, five (should have been six) Bartletts, a FlameBack Angel, and a Leopard Wrasse.
I had most of the equipment needed for the 'introduction' tank laying around, so the incremental cost was quite small, which made it easier to do. Not a perfect approach so I welcome suggestions!