we implement one for event registration. without queuing, you end up with some hidden complexity around whether a ticket in a cart counts towards the limit or not, and when it goes back into the available pool if that cart doesn't check out in time. none of it is too difficult to implement, but it is difficult to explain to users and creates experiences that frustrate people are or are perceived as unfair. for example, an event can be "sold out" while a payment is processed, and then the event becomes briefly not sold out again if the payment is declined.
a queuing system is easier for people to understand - you get in line, you have three minutes to complete your purchase when it's your turn, and everything that was available when you started your session is available until your session ends. people are still frustrated to have to queue, but at least they can form a mental model for what's happening.
IMHO a lottery system would be a better way to solve this, but event promoters tend to hate that and want a first-come first-served experience. i don't really understand why.