A use-case would be when you have a sidebar that you want to be resizable but only between, for instance, 50px and 150px wide, and you also want it to either be totally collapsed (0px wide or some other value) or between 50px and 150px wide. So if the user drags the separator past the min/max nothing happens. If the user drags the separator all the way to the collapsed width, then jump to that width.
(See macOS's Messages app or VS Code for examples of this exact functionality.)