N4obody would pay for advertising if all the traffic came fom natural listings in the search engines. Adwords is great for generating traffic quickly - at a cost.
The long term objective should always be improve the natural rankings of your sites and thereby reduce the PPC advertising spend. The problem is knowing which keywords to optimise on the website.
Which keyword research tool should I use and how do I use it?
Adwords is a great keyword tool. A well designed Adwords campaign cannot only earn you money but can also provide you with the very information required to improve the website and reduce your PPC spend.