Needs otoh aren't clearly delineated by the budget calendar.
My Dad told me how back in the 1970s he worked at a government-funded research lab. One time they called up a laboratory glassware supplier and said "We'd like to order $10,000 worth of glassware". The supplier asked "Sure, what specifically would you like to order?" The lab replied "We don't care, whatever you have in stock, so long as it costs us $10,000 and we pay you today – if we don't spend the money today we lose it forever".
They weren't allowed to amortise that, and any budget increase every three years would have been denied, so they had to include the whole replacement cost in every budget, and find ways of spending that money every year, or lose it.
Other way around. Right now there exists a negative incentive to go under budget, being that if you need extra budget next year you suddenly don't have a buffer.
The correct way to fix things is to simultaneously prohibiting end-of-FY budget-keeping purchases (e.g. by mandatory reviewing of purchases) while at the same time allocating a company/organization wide buffer for stuff that needs immediate / projected stuff that was not in the planned budget.
Obviously for common routes such as Sf to la, nyc to sf...etc they hard coded values.
for every $1 under the cap you received 50cent to use on a future travel plan over the calculated cap.
You could fly economy on an international flight saving money, then bank 50% of savings to buy a first class ticket some other time.
This created a negative feedback loop keeping travel costs in check.
"How many <Brand> laptops can I get for £xK?"
"What kind of spec are you looking for?"
"Don't care, just as many as I can get of 'something' for £xK."