Pros
If you sell a service, you usually don't have any inventory. Instead of buying and selling products, you convince customers to take advantage of your ability to make their lives easier. You do not have to manufacture, so you have no production facility, and you don't have to wait on products to be finished and inspected so you can sell them. This frees you up to focus on sales rather than inventory or manufacturing.
Cons
Your service business is harder to value than a manufacturing or retail company. Those businesses have inventory, equipment and other hard assets that have a value. You can start a service business with a phone and very little equipment. While this makes for a simple start-up it can make for difficult valuation. You have to establish a track record of sales and some reliable sales projections to convince lenders of the value of your company.