This article from Snews Magazine gives a good explanation of how a chimney sweep can provide a valuable service if you are buying or selling your home. A synopsis follows:

Many homeowners can rely on the professional expertise of a chimney sweep to evaluate their chimney properly. 

This inspection and any repairs recommended for safety will be considered a valuable asset for the home buyer of the property. 

If the heater venting system is sound, it increases the value to the homeowner. 

If there is a working fireplace, it increases the value of the property. 

If there is an appliance like a woodstove or fireplace insert inserted into the chimney, maintaining it is definitely of value in being able to share the details with the buyer. 

Excerpt from Snews Magazine, Chimney Sweeping News