My favorite use is putting user-defined attributes on data members, and using reflection to generate a UI to manipulate those values. I do it with these shadertoys:

https://github.com/seanbaxter/shaders#reflection-and-attribu...

Just mark your declarations up with custom attributes:

    [[.imgui::range_float {  .1,  5 }]] float Zoom = 1.5;
    [[.imgui::range_float {   0,  1 }]] float Speed = .15;
    [[.imgui::range_float {  .1,  1 }]] float XScale = .3;
    [[.imgui::range_float {   0, .5 }]] float YScale = .2;

Then loop over the members with a meta for, and emit widget code that's guided by the attribute kind and data. These attributes each define a scrollbar.

The kind of data you reflect over will likely come from within the program.