We keep last 7 years of hard copies on everything and do a shred / weed-out 2X a year. We have however kept all our 1040's ever since we started working as adults just for nostalgia if nothing else and in the case something ever happens to doubt our income existence in gov records. 7 years backlog is what I've always been advised to keep.
DW grandfather passed and we had to go through his stuff, he kept EVERYTHING, old posted checks, bank docs, receipts, you name it, he had two huge file cabinets full and several document boxes containg every paid receipt for utilities, bank loans, donations, it was overwhelming. One relative demanded that we go through everything piece-by-piece which was tedious and testing. We got to where we reached our tolerance level and turned it over to the one relative as we had gotten the most important docs to the necessary parties for estate settlement. To this day, there is one file cabinet still full of needless stuff which I think is a failure of closure on one person's part. I think she expects a hidden treasure map to fall out of a folder I suppose.