When I was using ArchiCAD, I was very happy when Graphisoft introduced this parameter... And then, several months down the road, I realized that I hadn't used it a single time in a real project situation.
Now that I've been using Revit, I have encountered a couple scenarios where I needed a canted wall. But, that wall did so much more than simply lean... It curved at the top to blend with a ceiling pad. It folded at the base, to integrate with some millwork. The profile was neither simple nor orthogonal. I ended up modeling it as an in-place family. That worked fine.
Here's the issue... Even if Revit Walls had a "Slant" parameter, it still would not have satisfied this particular design situation. The in-place family editor gave me much more control than trying to create it in ArchiCAD (that does have a "Slant" parameter).