If you bypass your computer completely, for reading,
then clearly you don't need Calibre. It can do nothing for you. The whole point of Calibre is to manage (rate, view, filter, side load, etc.) your vast library of eBooks stored on your computer. In broad strokes, it does nothing that the computer version of the Sony Reader computer software doesn't do, except for being more flexible on source and DRM.
If you manage your e library solely from your reader device and feel no need to insert a 3rd party into the mix, then Calibre holds nothing for you.
That being said, if you have a Sony PRS 300 or 350 (Or other side load only readers), or If you have multiple eReader devices, or an Android device that can recieve ebooks from a variety of sources, having Calibre acting as a sort of intermediary between various flavors is pretty useful to have.
Last edited by GlenBarrington; 12-06-2012 at 03:15 AM.