This is true whether you work with sheet or roll material. Since controlling the substrate impacts everything from image quality to diecutting accuracy, it's one of the most critical elements of any job you produce. So regardless of the number of graphics you print, you're working with one contained piece of material. A web-processing line can consist of various combinations of printing, curing, and finishing stations. And since the roll material requires no human interference between the time it's loaded and rewound after printing and processing, positional shifts and dimensional instability are automatically controlled.
Speed is another advantage.
Web presses are known for their ability to outpace sheet-fed systems, particularly when various processing steps are automated. Take, for example, a film for membrane switch overlays that features a removeable protective liner. On a sheet-fed printing line, the liner is peeled away by hand prior to printing. It saves time and reduces labor. And it goes without saying that a web system wouldn't be used to image a rigid substrate that cannot be rolled.