By default all the links are dofollow which means search engines can follow them and link juice would be passed to you but in case when a website owner does not want you to follow it send you a backlink with nofollow which means you are not to be supposed to get link juice.
To make your link nofollow one has to mention it.
Moreover google has announced that nofollow links would also be considered but with less impact.
Nofollow link position also matters.top of the page or bottom.
The term dofollow link is introduced in 2005 by Google, to reduce the search engine spam indexing and to improve the search engine results. Only Dofollow links pass link juice to the linked webpage and influence the target's page rank.
Dofollow and Nofollow, both are the types of link.
Nofollow and Dofollow both has their own importance.
Dofollow backlink helps in improving your site ranking while Nofollow Backlink helps to maintain the ratio of dofollow vs nofollow.
If you will only concentrate on creating dofollow baclinks then It will look unnatural which might be harmful for your blog.
So Both the backlinks are beneficials.
Do follow links will help you to achieve higher DA(domain authority) and PA(page authority), in turns improving your ranking whereas on the other hand, no follow links will not.