The is not a slush fund. It is a controlled cash advance against a defined budget, and it reconciles back to the penny.
A touring party needs cash on the road: per diems for band and crew, local parking, supplies, incidentals that cannot be paid by card at short notice. The advances a sum (the float) to the tour manager before the run begins. The tour manager holds it, pays from it, and accounts for every pound on .
When the float is run badly, two things happen. First, receipts get lost and cash evaporates. Second, the business manager has no idea whether the tour made money until weeks after it finishes, because the books cannot be closed without the float .
When it is run well, the float is sized against the budget, released in controlled tranches, reconciled show by show, and returned (or topped up) at settlement. The touring accounts close quickly, the tax treatment of each payment is clear, and the year-end is clean.