I think that the creation of blogs and portfolios allow teachers to reflect deeply on their practice and student learning. It is a journal of sort for teachers to explain concepts deeply or pose opinions on educational themes. In order to write about something you must really have the passion and knowledge to do so.
The reading of others' blogs is a great source of information and community. You can learn new lesson ideas or theories. You can stay up to speed on the latest educational trends. You can get inside the mind of some wonderful teachers.