I made a serious investigation regarding this issue and my conclusion is that not only that its NOT a waste of time but its also a MUST! yea, not less than that!
An important factor that Google-Yahoo-Bing check constantly is a natural proportions of backlinks type to the website. I would call it THE BACKLINKS BALANCE FACTOR.
Websites that has only dofollow backlinks looks artificial and will not achieve same results as websites that has a natural rate of nofollows backlinks among the total amount of backlinks.
Ideally, to make a strong backlinking impact to your website, you should keep the following 5 basic gold rules:
1. Keep a normal/natural proportion between backlinks that are dofollow to the nofollow ones.
2. the more backlinks you have the better.
3 try to create backlinks on websites that share similar interests to your website's materials.
4. try to create links on websites that enjoy's high google page rank
5. make sure to use the right keywords in you backlink anchor text