I entirely agree with what Caesar has said. I will add on that A: Despotism has a more immediate pay off. Some UHV's need you to move very quickly, and even when Monarchy averages out to higher output, sometimes getting some knights or buildings two turns early makes all the difference. B: Despotism doesn't just burn through food, but if used a lot it also burns through happiness (temporarily). If you have a higher happy cap than you know what to do with (either because it is so big, or because your city(s) don't have many tiles worth working so they don't need much pop, then despotism gets much better. C: Some buildings are important to get asap. For instance getting a forge, library, or market up early in a city can make up for lost output from whipped pop. Often when playing a european civ where you settle several cities at once that need similar buildings (usually forges) then a short period of despotism to get crucial infrastructure can be handy. D: In addition to Caesar's other listed examples, despotism isn't friendly to cottage economies. E: Finally, Monarchy is much more stability friendly overall. It has synergy with far more civics than despotism, including being apart of the powerful medieval vassalage synergies. The unhappiness from despotism is also one of the best ways to get instability from unhappiness (since the unhappiness has to come from a source other than population), while Monarchy oftentimes helps with generating the excess happiness that triggers "we love the king days" and giving stability from happiness.