Which frame are you looking at? Is it for machine quilting or hand quilting?
Look at the details of the listing. It is the poles that determine how wide the frame is set up. If the frame can be set up for 120" and 60", it means the listing includes poles of that length. If you want to quilt, say, a double bed size quilt, then you either need to set the frame up for 120" and use only the middle part, or you need a set of poles that will fit a double bed size.
In other words, 120" is the max when the frame is set up for 120". You could still quilt a baby quilt if the frame is set up for 120". If the frame is set up for 60", the max width you can quilt is 60". And that is for a hand quilting frame. If you are machine quilting, the available width is less than the poles because you need a free area for making bobbin changes, etc., on the machine.
To get the best advice, post the frame you are looking at and define whether you want to do hand quilting or machine quilting.