With displays increasingly getting higher and higher in resolution, having rasor sharp images is a must. While photos have to participate in the megapixel race, there's a lot of artwork out there that gets a much better effect if it gets stored vectorially.
I love Inkscape because it allows me to use multiple layers and easily create and place objects together. Fairly simple objects (like f.e. safety icons) are small in size, no matter what the dimensions of an image are.
A nice feature I love to use, is the option to import from PDF and then extract certain details.