"Our 15 year old patio looks almost brand new. You and your crew did a great job!"
Everyone can use more time in their day. Let the professionals do what they do best.
A professional has performed the service hundreds of times over years of being in business. They have seen every situation and can fix anything that may go wrong.
Specialized equipment makes the job easier. Don't spend your money on costly equipment that you'll only use once or twice.
Someone in the business knows what products are on the market. they've tested the different brands and know which work and which don't.
As a homeowner you may not have access to the same quality of products that a professional does. You can't just get it from Home Depot all of the time.
Some of the products used in restoration can be mishandled. When things go wrong, they go very wrong. Fixing issues is possible, but expensive.
Someone in the industry will have access to all of the newest technology, products and techniques. Professionals have access to training by the manufacturers - not available to homeowners.
Some of the processes take practice in what to do, what to watch for, what to expect in different conditions.