The main thing that the big G look for here is complete relevancy. If you are totally congruent with your keyword, ad and then landing page, then your quality score will be higher and thus your cost per click will be lower. This comes down to the very point of having your landing page optimized for the very keywords that you are advertising for. Makes sense right? When it comes to your ad, not only do you get your ad in bold where it matches the keyword, but Google loves you for this. So although this may be well known by now, many people still do not do it, and are throwing away money.