Well owning your own domain name with hosting has a bunch of benefits. For one, you can ditch the blogger blog, and upgrade to a much more customizable wordpress blog. Also, you can use your hosting space for images, videos, files, and storage. Plus it's much easier to tell people how to get to your website with the domain name instead of a blogger.com/blog or whatever it is. Or you can just redirect to your blogger blog and benefit from that.
If your blog turns out to be successful, you have built your own domain name up. You haven't built up the blogger.com domain.
Not only backlinks. How would you explain with backlinks that every time I write something on a non page rank blogger domain it is indexed almost immediately by Google and at the same time it takes weeks to index something written on a PR3 non blogger domain.