This shows people that you are a serious person, rather than someone trying to manipulate the group for your own ends. People online make a very clear distinction between a contributing member of a group and someone trying to take advantage. Offline this might not seem a businesslike distinction. Nope, not usually. But the butcher's shop is purely a business.
Online forums are discussion areas first and foremost.
They are not established to be commercial venues. The distinction is very valid in this case. Consider it the online equivalent of getting to know the neighborhood. If you see that someone has a site that complements yours, offer to exchange links. Or just put in a link to theirs and let them know about it.