A low cost per click affects your return on ad spend directly!
Setting a low bid is just one way to lower your cost per click - and probably not the most successful! A good keyword quality score is more important than a low bid. The better your quality score, the lower your cost per click and the higher your return on ad spend. Of course only, if you have conversions on your website.
Use Googles conversion tracking to monitor the number of conversions and the cost per conversion. This is an easy way to keep track of your advertisements performance. After all you want your website visitors to sign up or buy products on your website. Just having traffic is most likely not your websites goal.
Check out the video and learn what variables are important for successful online marketing!