In my opinion the people who write blogs who would like to show their skills/abilities and thoughts in a specific area as a constantly updating and changing log based on recent events and things created/discovered. These people as those who wish to speak to an audience (and to themselves) recording things for later use, I see them as individuals wanting to get their thoughts/ideas and comments across to other people. The people who enter things in blogs I would think that its only an individuals point of view but I'm sure there are blogs where its a discussion between a group, these people are those who are confident writing to an invisible "relative" audience and want others to view quite often keeping track of the life of the person. Its a personal space where people can share everything and anything that they experience and want to share with others.
I find it to be quite a strange thing really as its something that I haven't really done before, only in sketchbooks during projects but not posted so that everyone and anyone will read and see. It is a good opportunity to keep a record of thoughts even if they are not read again for a while, writing to me seems the best way to add current thoughts and ideas as mentally to record them helps justify them and can inspire questions like "Why do I think that?" which can then be explored. I'm not sure if I like the idea of anyone and everyone reading my thoughts but its just chance that people will be able to read and see them and if not for an invisible audience for myself it would be useful.