JPEG Format
Inkscape has historically been very reluctant to help users make jpeg files directly from Inkscape. It's native output format of PNG could always be converted externally to a jpeg file, but having the format supported natively was a user request for a long time.
The problem with the format is that while the file format is good for photos, it creates artifacts and distortions in logos and other flat vector images. This is because of the nature of the mathematics, the high degree of contrast between adjacent pixels in many vector graphics as well as the angles of lines. Some jpeg files can look perfectly fine, but contain imperceptible defects, while others are distorted terribly at the same compression level.
If you export using the new Jpeg Raster exporter, your artwork will first be rendered into a PNG file, and then this PNG file will be sent automatically to an external program which does the conversion for you. A popup window is provided to allow you to adjust the compression level and other jpeg settings which are then sent to the external program. Inkscape itself continues to not do jpeg compression internally.
Transparency will also be lost from the image when exported. Be sure to set a solid background when exporting to raster formats that don't support transparency.