Imagine in perspective view an object like a book, its bottom edge nearest you.
I have need of keeping the bottom edge horiz whilst rotating it downwards to see more of its front cover and also get more of an oblique aft view of it. ( seeing more spine in other words)
If I use the normal perspective rotate tool I lose the horizontal bottom edge, it tilts.
If I had a gumball type control I could rotate to see more cover, then rotate to get a more oblique aft view keeping the bottom of the book still horiz.
Note I am wanting to move the view, not the actual object !