Grouping in a grid can also be saved to views on a page with large view selectors. However not on pages that have a small view selector. See https://learn.microsoft.com/en-us/dynamics365/fin-ops-core/fin-ops/get-started/saved-views#switching-between-views

When looking at purchase orders in fashion where you have a lot of product dimensions on an Item you want to group by item and maybe style and/or color to know what sizes and amount of SKUs you have in your PO. you can do this by grouping on the appropriate columns, however you can't save the view. So each and every time that you go to POs again you have to create the proper groupings instead of getting them from a saved view.