If you have multiple smaller and simple 5250 application sessions in VLF-WIN and VLF-WEB, you cannot navigate between destinations defined in different sessions. The ability to navigate from everywhere to everywhere by having a single large navigation tree has often been the motivation for creating a single large and complex 5250 application session.
This design issue does not exist in VLF-ONE applications because navigating to different 5250 destination screens is achieved by switching (or invoking) the target business object instead.