More than one Blog?

A quick post before the end of the year triggered by the holidays and vacation trips: Is there a reason for having more than one blog? There are many!
What if you want to keep a record of family trips? or what if you want to carry on with a specific project that you want to record things about? Such as a charity event, ot a product launch. 
Blogs don't have to be never ending records of your life or your work. They can certainly be short term projects with a defined goal. Here are some examples:

• A record of my family trips (http://travel-record.blogspot.com/)
• An expedition to go to the south pole and teach children about it (http://southpolequest.com/)
• A product launch (http://techedgeweekly.com/)