I often get started with a website and need a Vector File for the logo. This is very important, as I can make it as big or small as I want to without loosing quality. But it appears to be jargon to most of my clients.
If you look at the sample below, it shows the difference between quality of enlarging a JPEG image and a Vector Image. A JPEG image can’t be enlarged unlimited, but Vectors you can.
It’s a good idea, when you get your logo designed, to ask for the .eps file, as Graphic Designers can open that in any of the programs they use.