It depends on the finish. As a part of the process, we use sealers on all of our stamped concrete. While we typically do not recommend sealer application for exposed aggregate, or washed finishes, it is not necessarily harmful and is largely a decision of the customer. Typically, you do not use sealers on broom finish concrete.
The benefits of sealing concrete are largely cosmetic, but it does have a marginal impact on the concrete’s durability in that it reduces the amount of water that enters through the surface of the concrete. It helps keep the surface clean and uniform in appearance and in some aspects easier to maintain. Aesthetically, the sealer typically darkens and enriches the concrete’s appearance, giving the surface a “wet” sheen. Sealing both older and new concrete sections that are adjacent is a great way to achieve some continuity in the overall appearance.