Pros of search engine marketing
Everyone loves free marketing and this is often counted as free marketing. Indeed, as traffic arrives on your site it is free and quite often highly targeted. So the main advantage is that it is free. If you can do the work yourself, then it is highly rewarding. Suddenly finding the traffic rising on your website and hundreds of new hits each day makes you feel really good. It can inspire you to further efforts.
It is not as technically complicated as people make out. These days tweaking the code behind your website is not the art it used to be. As long as the code is half decent you should get there. So another pro is that you can do the work yourself just by writing articles and posting to blogs.
Cons of search engine marketing
Unless you are a small business and know enough about search engines, Search Engine Optimization is not actually free. You need to pay someone to link build or article write for you constantly. The bigger your business the higher volume the target keywords need to be generate sufficient traffic and therefore the more competition those terms will have. This means a lot more work to get well positioned.
There are no guarantees. No matter what self confessed search engine optimization experts will tell you to get you to sign up to them, there is no golden bullet to get you into top position and they can not guarantee that the work they put in will get you to the top page, let alone the top position. You could put all of the work in, or pay someone to put all of the work in, and never get to the position you need for the traffic.
You are not in control of the success of the terms! A slight change to the major search engines and you could plummet from your hard earned first page slot to somewhere that no-one will ever see you. It hurts to see you hard earned work come to nothing and when your site slides down the rankings your traffic will suddenly dry up.
You also can not throttle the marketing so in quiet times there is no way of speeding up the traffic and in busy times it is not possible to pull advertising to reduce the leads coming in.
Overall, getting traffic is rewarding, but it can be unreliable, difficult to achieve and erratic at best. If you rely solely on the traffic sent to you from Google, MSN, Yahoo and the likes then you could find one day that a change to a search engine leaves you without any new visitors. So use them with caution, but do use traffic from the search engines.