Many times a person's first blog won't be their last. They start with a specific idea and as time goes on, they grow and that idea changes. It's not uncommon for people to start on one blog and either switch to another or start up a second.
Once you learn you way around one blog, adding a second is pretty easy. You've already figured out the little tips and tricks to help save time and money, so when things get a little stagnant or you want to try out a new subject they start out a new blog.
There are several ways you can do this. If you don't want to purchase a domain, then you can choose several free blogging platforms. This is particularly helpful if you don't plan on a lot of monetizing. Many of these free places won't allow you to have advertising, etc. on the page and instead will put some of their own ads.
If you do plan on monetizing, then purchasing your own domain is the way to go. You can always use the same content management system as your other blog, but if you're interested in learning more or trying out something new, then feel free to switch. There are several content management systems available for free including Wordpress and Drupal.
When you have more than one blog, you can't let one override the other. You have to keep up with both blogs and maintain a set schedule. Don't think that just because you posted on one that you don't have to post on the other.