Check out this overview video here on mobile site, I think it may help
answer your questions:

http://www.prophotoblogs.com/support/mobile-site-overview/

Basically, the option allows you to create a different mobile specific
site that can be viewed on iPhone, etc. However, you don't create a
different page per se for a mobile device, your blog just renders in a
different way (per your customization settings) on that device type.

As for iPad, we actually need to change that wording because enabling
mobile sites doesn't show the mobile version on iPad (only on phones),
however, by default ProPhoto 4 does display slideshow galleries
different on iPad than on a computer. (This is because of the whole
touch screen functionality, we've tried to make viewing galleries on
iPad more touch/user-friendly than the options on desktop.) I think if
you go to any of the demo examples on our blog and view in iPad and view
the slideshow gallery, you can see this.