Today a lot of companies have mobile versions of their web site. Much of the time this means a different layout too. Changing the mobile layout to a smaller, simpler one helps the page to load fast on mobile devices. However the change can mean making certain features of the site inaccessible on mobile devices (or at least some devices) because they just aren’t as functional on a smaller scale.
One example of this is Shutterfly. Shutterfly’s mobile site makes it easy to create albums from the pictures on your phone (including ones from instagram and facebook), order some of their photo gift/canvas items, and order prints. They even have special sizing options on the mobile site for instagram photos. However you have to go to their desktop site to have access to their full range of products including the photobooks (It does give you information about them though). The photobooks have to be “designed” in way. The layouts get picked, choosing the pictures for each page, and adding things like sticker and typography to personalize it. This is much easier to do on a larger screen and on a faster computer.
This can work the other way as well. The file-hosting service dropbox is really only usable on their mobile site or apps. The desktop version of the site only prompts you to sign up or sign in. After that the only options are to choose a plan and download the program.