Comment by mitchdoogle

I have an old Kindle and it's always had trouble trying to just load files over a USB connection - books show up in the wrong section, no metadata, etc.

Calibre makes it simple and the books appear properly on the device. And it can fix metadata on books downloaded from the internet. That's the main reason I use it. Add in the fact that it's a nice management tool for seeing all my books at once and I'm very pleased with it.