Let's try to sort out that. We have two different apps here: Navigator and ProjectWise
Navigator apps are for reviewing your drawings on your iPad. Navigator Mobile almost replaces Navigator Pano Review. Most probably Mobile version will replace Pano Review completely in the future. Mobile version supports full 3d while Pano Review supports only panoramic views (3d from predefined points). Pano Review version allows to mark-up drawings in your app. Mobile version does not allow that - at least not yet, actually I'm not sure if that's possible. Most probably it is but I don't want to make unfounded promise.
ProjectWise app is for getting your drawings into iPad from ProjectWise Integration Servers.
So basically imagine you have iPad and get into the field/construction site. Field worker says that there is problem in sector B so you go with iPad into sector B, connect to ProjectWise server using ProjectWise app and download Navigator Mobile drawings for sector B. Then you open drawings in Navigator Mobile app and can compare what's different between drawings and real situation in sector B and successfully identify what has caused the problem.
While a little bit outdated http://www.bentley.com/en-US/Promo/iPad/ contains a lot of useful information.