German cockroach, pharaoh ant, cat flea, pantry moth: each species has its own hiding places and weak spots. Spraying insecticide at random often just pushes them into another room, or next door, without reaching the colony.
The technician first identifies the insect and finds where it shelters: hinges, appliance motors, skirting boards, service ducts. He applies the product as close as possible to those refuges, as gel, dust or a spot treatment, then seals the cracks and pipe gaps the insects use as corridors. In your kitchen or a restaurant's, there is no need to empty everything.