Blogging has been referred to as journal keeping, grassroots journalism, and even free advertisement.  The possibilities for blogs go far beyond what the average person may first think.  Blogging was one of the earlier forms of social media to exist on the web. 

Bloggers have many different motivations.  There are fine main ones that include: "documenting one's life; providing commentary and opinions; expressing deeply felt emotions; articulating ideas through writing; and forming and maintaining community forums."  There are other types of blogs, but those 5 motivations are the reason for the existence of most blogs.

Documenting your life
Many bloggers recorded their lives on platforms such as blogger before more recent social media platforms existed.  They could utilize a photo album gadget within the blog site to share photographs, and could enable commenting on pictures.

Catharsis
Some feelings can be difficult to describe through speech.  I personally find some concepts of emotions easier to explain through writing.  Blogs are often utilized as either private or public emotional outlets for bloggers.

Commentary
Social commentary is another main purpose for blogs.  In the late 2000's I know many sports blogs would provide opinions (as well as facts) on sports gossip, scores, rankings, and draft stats.  These have since become less popular, but sports was definitely one of the more popular opinion blogs.

Muse
Authors may blog because it will stimulate their creativity.  Some say the best cure for writers block is to "start writing".  It doesn't have to be about anything in particular, but if you start writing something, your mind will be stirred to create.  Some people use blogs for that purpose.  It may not necessarily be nonsense, but the posts could be covering a variety of topics.

Community Forum
Blogs utilized as a community forum sprang up once commenting on blog posts became the norm.  The article "Why we Blog" discovered a forum for poets, two for educators, and one political discussion in their preliminary search. 

This article is a bit outdated, since it was published in 2004.  Facebook, which is the currently largest social media platform was only launched in early 2004, and was exclusive to very few users (specific universities).  The number of bloggers has declined because of the rise of social media platform software.  They still exist, and are a tight knit group it seems.  It will be interesting to see what the future holds for blogging.