Do you ever need to produce receipts for AFIP or proof of purchase? It would be awful to accidentally throw out deeds or checks that are lost in a pile of empanada delivery and Royal Canin receipts.
For deeds I suspect the problem is you have to have the original to prove ownership. Although MIL used to be a notary why the hell she needs to hang on to such things for ruddy years and years is beyond me.
As for the wfe keeping receipts...that's to keep and eye on the supermarkets/banks who have a history of ripping her off.