The two most important reasons for sealcoating are:  

Preservation of your asphalt and to enhance your curb appeal.

The primary reason for sealcoating is to protect asphalt from the sun and water as a part of preventative maintenance.  Over time asphalt oxidizes and loose some of it’s flexibility.  This in turn will make the asphalt brittle and begin to crack.  If not corrected, over time water will penetrate through the cracks, which could result in deterioration of the existing sub-grade.  Seal coating is an inexpensive process that will maintain the asphalt by providing a water resistant layer which will slow down the oxidation process.