Benefits:

• It's free
• You have total control over your own marketing
• You get to learn a new skill

Risks:

• You might not be that good at it. And if you don't know what you're doing you could accidentally end up using 'black hat' SEO techniques that could get your site banned from the search engines.
• It's not actually free- it takes time... lots of time.
• You're not guaranteed any results. Although most SEO consultants won't promise instant results, they should be able to give you a guarantee of results over time.

It's a case of weighing up how much spare time you have, how much money you have and how much patience you have. Then decide whether you want to take control of your Google SEO campaign.

If you've decided that you are going to handle it all yourself, then get a good book, keep yourself informed and stay away from black hat SEO.