Having a regularly updated blog on your site with a decent history of posts can be valuable in link outreach. A lot of the best link acquisition tactics are based around producing content that other sites want to link to, and a blog gives you a logical place to publish all that content.
But more than that, all those small and medium sites you sifted through in your prospecting that had blogrolls might well add you to their blogroll as well. This gives you the advantage of a sitewide link — a link that is usually on every page of their site — which maximizes the PageRank that flows to your site. (Some sitewide links can look spammy, but blogroll links are good links, and a standard within the blogging community).
Asking for a Blogroll Link
The best way to ask for a blogroll link is in an email promoting another piece of content you created and published on your blog. So if you put together an interactive map showing the preferred dog breeds in each major city in the US, you could email dog bloggers (there are more than you’d think) and tell them about your neat map, then also ask for a blogroll link if they think it would be a good fit.
It’s worth noting that before you ask for a blogroll link, you should first ensure that you’re blog has a decent amount of good quality content (a minimum of 12 good articles). No one is going to put up a blogroll link to a blog with only a few posts.