Sure, it’s easier to use a free host for your blog at first. Minimal startup time with WordPress.com or Blogger and you’re off to the races!
But you’re not in control of your own destiny.
For WordPress.com, they won’t let you advertise or put up affiliate links to 99% of the programs out there, and you can’t add plugins or custom themes to your blog.
Blogger allows ads and slightly more control over the blog, but then your content is really owned by and at the whim of someone else and it’s hard to differentiate yourself on Blogger. You can’t easily redirect or mask affiliate links and all the blogs look more or less the same.
Go to Godaddy, get a domain name for $9.50 and host it for free until you’re ready to pay the $4 a month to upgrade it. If you do anything even a tiny bit right, you’ll be able to cover that $4 a month in your sleep by the second or third month.