Hard drive space increasing?

I don't think this is an issue, but wanted to make sure. My mac crashed early this week and lost everything. This made me finally install time machine. Since I'm back on my new mac drive and finished installing pretty much every app I lost, my space has been increasing over the past couple of days. It went from about 410GB free to 480GB free right now. It already grew by 4GB since this morning. Any idea what it can be, and if I should in face be worried?