Depending on the treatment. If it involves spraying you have to leave the space where sprays are being applied at least for a couple of hours. However, you will be instructed beforehand according to your personalized service.
Pests reproduce extremely fast and they are even better at hiding from our sight. Seeing an individual one is almost always a sign of an infestation on the premises. When people try to handle the problem themselves, they might get the ones they see, but are usually inefficient in getting rid of the entire population, as it’s always hidden.