No. If you dereference a widget completely, the garbage collection will free up memory. It may not always be instantaneous, it may take 30 or so seconds for it to happen. If it does not, the widgets are referenced somewhere. Assuming you’re not using version as ancient as 4.17…
Regarding something like an inventory or any reusable widget, hiding/showing is better in most cases, indeed. Adding / removing from parent may also be an option in case you want to re-run the widget’s Construct Event.