I always quarantine new plants that I get. Just to be on the safe side and observe the plant for a few weeks. Pretty much I try to avoid getting very distressed plants.
Some I can experiment to see if it will survive with gentle care if it seems it was just bad watering issues. It does allow me to learn about the plant's resilience. But some are just too sick and a sick plant harbors more pests already.
Once I see the quarantined plant responding well to watering, and get to see if there are critters aboard then I spray. Too much spraying at times also adds more distress to an already sick plant. At the same time, do not apply fertilizer yet. Give it time to fully adjust to your growing environment. A lot of failure also comes from that, over eagerness to fertilize at the wrong time especially when plant is already looking sick after a few days of being brought home.
