If you choose to have a blog the assumption is that you want to share information (visual, written, aural) with an online audience.
A blog is a creative outlet. It allows others to see what your interests and focus are. This includes your ideas, and ideas you've found through research.
It's useful as a record of academic research, college course output and as a specialist reckoning of thoughts and visualisations.
It's a useful place where others can find your visual creativity, reflections and research.
Others can communicate with you about your work through your blog.
It can help establish your reputation, or specialism, or knowledge base.
You can use its existence as an aid to applying for higher level courses and/or finding a job - if the content is relevant.