I do support this Idea, I think it is really necessary, mi idea of this functionallity is that in a module or view (grid in a page) can appears icons of '+'or '-' just like appears when have them in the tree view of a list. so we can group or collapse when click on them, this could facilitate the administrators experience, avoiding to create additionally filter modules
I do support this idea too. In my experience, it would be particularly useful for line items (or at least line item subsets). In financial statements, it would very handy to be able to show or hide easily some details that you don't want showing all the time, while keeping the important line items showing.