Printer drivers have come a long way, and are generally very good at what they do, with one glaring exception. If the image aspect ratio of your image for print is different than the paper aspect ratio (and they almost always are) the driver cannot read your mind about how to crop. It will have 2 settings in this case: 1. Print full size (which will put the entire image on the paper, but leave white space on 2 sides) or 2. Crop to fit (which will cut off some part of your image, an equal amount on the shorter sides, which may remove some elements of the image which are important, or completely change the look). It won't leave white space on only one side, and it won't only crop from one end.
This is what makes it better for you to get your image set up in the editor of your choice for the print size you wish to use. You don't absolutely have to, unless you want complete control of how the image appears on paper. Who doesn't?