I personally think a QT is 100% required. I run my fish through a protocol that I've learned from R2R reefers that takes about 6-8 weeks. So far, over a year and extremely healthy fish. Quarantining is simple and doesn't have to be expensive...10g tank, HOB filter, small heater, thermometer, airstone and pump, egg-crate lid, and few meds. No light is required.
I know of a friend who never quarantined...one fish wiped out his 300g tank with velvet...
If you aren't medicating, then maybe at least a small setup to monitor the fish for a few weeks at least to ensure no noticeable signs of disease.