There's really only one pro: getting better rankings in the SERPs. Cons: not good for people who hate ranking well in the SERPs.
pros is that ur site get natural search rakings and pros is that it takes time to get that rank wen compared to ppc
Actually there is a CON ---- Wasting time and/or $$$$ If you spend your efforts or $$$ targeting terms that ultimately bings in little in the way of traffic and utlimately conversions, you can't get it back. Not all #1 rankings are created equal ya know..... it's all in the initial research :0) So there is at least one downside... you do it wrong and you've wasted resources.
Pro: Save PPC $$$, increase traffic Cons: none for white hat SEO. Black hat seo can back fire and screw the pootch.
There are cons to even white hat seo, and that is time investment. If you plan and research the wrong keyword's, then spend months to rank well for them to see it is not bringing in any money. That is one con to me, and yes even the best companies can miss target on some keywords. Unless of course you don't mind wasting a lot of time, then I guess it won't matter.
Pros: You can get good amount of traffic to your site Cons: Results take time, and the process is very time consuming
PROS: (free) traffic, builds strong brand, sales away from competitors, increase CTR on paid search campaigns, potential for a high ROI,... CONS: (can be) time consuming and potential to actually cause reverse and have site rank much lower