I know some people that take quarantining to a whole new level. After the fish is through the initial period, rather than be added to the show tank they add fish from the show tank to the quarantine tank. They want to control their risks. I have had only one instance where newly added fish that had been quarantined wiped out previously existing fish.
125 - BGK, pictus cats, silver dollars, kissing gouramis, palmas bichir, delhezi bichir
125 - Red severum, bolivian rams, Turquoise rainbows, irian red rainbows, loaches (angelicus, zebra, kuhli and horseface), plecos (BN, RL and clown), denison barbs, pearl gouramis
90 - Congo tetras, african knife, elephant nose, spotted ctenopoma, upside down cats
QTs - 29, 20H, 20L, 10