Why do my spreadsheet formulas keep breaking?
Because a formula like a VLOOKUP is holding two lists together by matching a name that somebody typed by hand — and sooner or later they type it slightly differently, move a column, or insert a row in the middle. You can patch it, and you will be patching it again next month. PaprPlain does away with the whole arrangement: an order simply knows which customer it belongs to, and a payment knows which order it is against, so there is nothing to match up and no formula to break. Open a customer and every order of theirs is sitting there; open an order and it tells you whose it is. You can even rename the customer and nothing anywhere stops working.
Nothing to drag down
An order adds up its own lines. Change one and every total above it follows. Try to delete a customer who still has orders and it tells you what is in the way.