Blog Comments can be a great help in converting first time visitors into subscribers. Because if someone is new to your site, he may get a good impression when he sees lot of people commenting on your blog posts.
Now the reverse is true is well. If most of your articles have no comments, it is likely to turn away new visitors as they will feel how unpopular your blog is.
SEOmoz has some great tips for blogs that are new and have yet to make a mark [find subscribers] in the blogosphere - Launch Without Comments (and Add Them Later)
Don't offer the ability to post comments on the blog and no one will know that you only get 20 uniques a day. Once you're upwards of 100 RSS subscribers and/or 750 unique visitors per day, you can open up the comments and see light activity.They have a similar advise for contextual advertising - Eschew Advertising (Until You're Popular)
You wait until your blog has achieved a level of success before you start advertising. Ads, whether they're sponsorships, banners, contextual or other, tend to have a direct, negative impact on the number of readers who subscribe, add to favorites and link - you definitely don't want that limitation while you're still trying to get established.When you have little or no traffic, the advertising dollars may be short enough to buy you even a bottle of coke. So why trade those precious traffic and prospective subscribers for a few cents ?
21 Tactics to Increase Blog Traffic [SEOmoz Blog]