If you are planning to sell your home you may wish to have an inspection prior to placing your home on the market. It will give you a better understanding of conditions, which may be discovered by the buyer's inspector, and an opportunity to make repairs that will put the house in better selling condition.
If you are purchasing an older home you will probably want a home inspection performed. In fact, some lenders and types of loans require it.
A home inspection is an examination of the structure and systems: heating and air conditioning, plumbing and electrical, roof, attic, insulation, walls, floors, ceilings, windows, doors, foundation, and basement. No house is perfect. If the inspector finds problems, it doesn't mean you can't sell or buy the house. You may or may not want to make the repairs and you can always adjust the selling price or contract terms if the problems are major. This information will also help you determine what type of financing will or will not be available for the home.
You may wish to ask if he is a member of the American Society of Home Inspectors (ASHI). It is a non-profit professional association which has developed "Standards of Practice" and a professional Code of Ethics that it's members are required to follow. Some states have their own organizations like the GAHI, Georgia Association of Home Inspectors. You may also want to ask if he is a member of the local Better Business Bureau. Always find out how long they have been in business, and if this is a side-line or their major focus.