When working at a helpdesk company managing IVR services, one quicly learns :<p>LIFO minimizes latency and resource usage
FIFO maximizes latency and resource usage<p>What you want to serve, as a queue manager, is the largest amount of requests in the shortest amount of time. Counterintuitively, this means that you absolutely don&#x27;t want people who wait a long time in line to get served, because if they&#x27;re willing to wait on hold for 30+ minutes they&#x27;re willing to badger your agent (the guy answering the phone) for a long time into doing what they want. The result of this is that the queue quickly gets taken over by these long-waiters and everyone else gets delayed massively.<p>What you want to maximize is requests served&#x2F;agent time. Requests served is what brings in the money, agent time is money leaving. LIFO, combined with seriously incentivizing agents to make sure calls get resolved faster than $avg - 10% or so, ideally with a pay bonus (people, especially people in low-end jobs, respond very strongly to pay bonuses).<p>The net result is that complex requests will result in waiting very long in the queue (because agents will throw you back to the queue as soon as they realize what you want is complex or impossible (people wanting things you can&#x27;t provide are very bad in all respects, very common, and the people requesting them usually have way too much time). &quot;I want to talk to manager&quot; -&gt; just throw him back in the queue). This means complex and impossible queries really, really start taxing the customer&#x27;s willingness to sacrifice their time. Ideally this would result in the 2-hour-long &quot;pay for me sending a slightly scratched product I bought last week in the US for 5$ less than I could have it in Antarctica, and let me ship it for replacement in &lt; 1week, or I will #$)(!@#%)! 1@#)$&amp;!@)#$ @$#)@&amp; @)$&amp;)<i>#@&amp; you and your entire family you !#@$ (@</i>&amp;@)(#&amp; #)(<i>&amp;</i>@)&amp;@! #)(<i>@#)(</i>@&quot; conversations to just not happen. Normally there&#x27;s a lot of these, they wear out agents (people being treated badly by customers to the point of crying happened almost daily)<p>Now you don&#x27;t quite go for straight LIFO. Firstly a lot of people are offended by it, think it unfair, that sort of thing (and then the costs start mounting). You also don&#x27;t want pure LIFO because there are customers that you actually want to serve with complex queries, so you start building a complex multi-queue system, but the entrypoint is usually a LIFO queue.