As much or as many as one wants; without limiting quantity—used to indicate any amount desired.
このケーキは欲しいだけ食べていいよ。
You can eat as much of this cake as you want.
子どもはお菓子を欲しいだけ取って、喜んでいた。
The child happily took as many sweets as he wanted.
予算の範囲で欲しいだけ購入してください。
Please buy as many as you want within the budget.