The main reason to hire a pressure washer service is safety. Pressure washers use chemicals along with the high pressure, which can be very dangerous and hard to control.
Along with safety issues, there is the damage that can be done to a home if the pressure washer is used incorrectly. Concrete can have chunks taken out of it, meaning that driveways or walls may need to be redone or completely resurfaced to repair the damage. The cost of buying a pressure washer and all of the correct attachments to do the job a homeowner needs, coupled with the possible damage and repairs can make the cost of hiring a professional seem very reasonable.
The pressure washers that consumers can buy at their local home improvement may not be able to provide the correct pressure to get the job done. It may also not have the right pressure to reach the roof or high areas without the dangerous task of trying to haul the washer up a ladder or scaffolding.
There are things to keep in mind when hiring a professional. The company needs to be insured. Ask if they are bonded and have workman's comp for their employees. Certifications and references are important. Be sure to check references from previous clients.