The answer is it depends...
In our office we have cosmetic dentistry patients who fall into two different Zoom whitening categories.
One group wants to just get in and get it done. They don't want to tinker with trays at home, or they want to do whitening before a big event and just want to do it quickly. For these patients we typically don't want trays and they are not necessary for Zoom.
The other group wants to get a really nice result and wants to have the ability to re-whiten or touch up at home whenever they want. For those patients make trays. There is a different cost, but we always talk about the option up front, so they don't have any cost surprises.
As with all procedures, you have a choice and the choice also affects the final results. Make sure to discuss what sort of result you want from your cosmetic dentist.
Thanks, Scott Greenhalgh, DDS