Perspective comes in two three licenses, which I think may be part of your confusion. The mobile-only license will only run inside of the native mobile applications (iOS and Android) and is part of the ‘upgrade’ for total-care customers who purchased Mobile module licenses in <8.0 [1]. The full Perspective license allows any device (desktop, phone, tablet, etc) with a modern web browser [2] to launch the same Perspective resources/projects/views.
EDIT: Three licenses, actually - Mobile (native app) only, browser (no native app) only, or both combined. The ‘migration’ path from existing Mobile module licenses still stands - a 7.9 Mobile module license + a total care contract = a Perspective mobile-only license in 8.0.
There’s no additional effort required to “port” a Perspective window to/from desktop/mobile. There is some additional, front-loaded overhead in terms of UI design, in that you have to design your projects around being able to resize from small, portrait-oriented mobile devices up to large, landscape desktop resolutions. The tools available in the Perspective designer are what helps you do this. I would definitely recommend checking out Carl’s overview of the Perspective module [3] and, if you have a ticket/can sweet-talk your sales rep, the Design Principles for Creating Mobile-Responsive HMIs video is also a great resource for learning about that extra design work.