Spreadsheets fail at the third vendor, because Indian vendors do not invoice once.
A caterer takes an advance, a second payment, and a balance on the day. A single "₹6,00,000" column tells you nothing about what leaves your account next week.
They differ more often than anyone expects, and the gap is easier to argue when you have the advance receipt.
Otherwise you find out what the sangeet cost only after it is over.
Pandit dakshina, transport for out-of-town relatives, room nights, staff tips, return gifts, and the generator. These are where the overrun lives.
When three people can commit money, the budget is already gone. One approver above a threshold.