It's all about risk....you risk putting them in the tank and losing everything to Velvet if you don't quarantine. If you don't do quarantine correctly (or even if you do) you risk stressing the fish to the point of death. Assess your risk and do what is best in your situation.
Here's another thought: buy fish from sources that quarantine. Will cost more but worth every penny. Again, still a risk there but it is definitely minimized.
Here's another thought: buy fish from sources that quarantine. Will cost more but worth every penny. Again, still a risk there but it is definitely minimized.