Deciding whether to buy now or wait for a future sale comes down to a few practical factors - how urgently the item is needed, and how predictable that category's sale cycle actually is.
Some categories - electronics, seasonal clothing - go on sale predictably at specific times of year, making it easy to know whether waiting a few weeks is worth it. Others rarely discount meaningfully, making "waiting for a sale" mostly wishful thinking.
An item needed immediately - a broken appliance, an urgent purchase - has a real cost to delaying beyond just money, which should be weighed against the size of a potential future discount.
Deciding beforehand what discount percentage would justify waiting removes the temptation to keep waiting indefinitely for an even better deal that may never come - a clear threshold makes the buy-or-wait decision much easier in the moment.