I expect you might respond with stating I have to level the pano before rendering
Yes, that's the way to do it, and it's very easy to do with the vertical line stoll in APP/APG - as I expect you know already?
but things are not that simple sometimes.
Why not? You have to stitch and render a pano before you can use it in APT to create a tour.
Yes I should do everything perfect, starting with placing my tripod perfectly level and check the leveling in APP before starting the rendering.
In my reality I am always in a hurry and do not have the time to check every .pano that is created from every group loaded into APP (sometimes 20 in one batch). Often there is no need to level. But the few pano that are not level are often only noticed while working on the tour. Being able to correct the roll a few degrees while working on the tour would then be much faster then having to go to the pano-editor and regenerating the pano in question.
Also, at the end of a project I want to have a meeting with client to go through the tour. When we find a not level pano it is very handy to be able to correct directly in the tour and not having to wait for the pano to regerenerate.
So it is a time and business motivation.