Depends on what you blog!!!
Let's say if you do a very poor job at blogging IE: only advertisements and sales pitch everywhere. People will ignore this type of blog and whatever you promote is probably going to have a negative connotation instead of a positive one.
However, if it's a flip of a coin and you do achieve a great job at it. It's a great way to promote your site for free!!
Remember, you got one shot at blog. If your visitor don't like your site, they will most likely NEVER come back to your site. However if you do a good job at blogging consistently you might just get a customer of a lifetime. You never know!