The blogs that already exist that allow you to use their services are already optimised.... yes?
So having your own blog (using an existing provider) means you get SEO for free, as it were.
In the case of Blogger, they add every idea they can think of. Believe me, some of these are not good ideas! Blog description at the top of the page makes every post look the same. It is SO easy to add (too many) labels and hence duplicate your content => the supplementary index
If something is a really good idea, the pros will all be doing it, so check them out