It was common enough. For example, Jacques I, Emperor of Haiti (1805), Ferdinand I of León, Emperor of Spain (1037), Simeon I, Emperor of Bulgaria (913), Ferdinand I, Emperor of Bulgaria (1908), Stefan Uroš IV Dušan, Emperor of Serbia (1346), Bokassa I, Emperor of Central Africa (1976), the Gwangmu Emperor of Korea (1897), Bảo Đại, Emperor of Vietnam (under French colonial rule), just to name a few.

There was often significant "title inflation", with rulers adopting more and more grandiose titles, often as their real power declined. Consider the Timurids: Emir Timur ruled with a modest title (partly because, not being a Genghisid, he didn't take the title of khan; his ruling children and their descendants were all Genghisids, and many ruled as khans), and by the time his descendants were reduced to ruling single cities, some were using the title of "padishah", "emperor of the universe". An Indian saying went: "If you rule a single village, you are a rajah (king), but if you rule two villages, you can call yourself a maharajah (great king)".

In some cases, the claim of emperorship was justified by having conquered other kingdoms and having incorporated their territories in one's own. Sometimes, sub-kings ruled under the emperor, or foreign kings paid tribute. This could occur on a quite small scale, and led to some rather minor emperors who could plausibly claim the title. Other claims were unjustified, and appear to reflect ego rather than reality.

Often, there was little benefit and substantial potential costs. If adopting the title of emperor was obviously unrealistic and meaningless, it would not be taken seriously, and could make the emperor the subject of ridicule. It could endanger foreign relations through being seen as a claim of equality or superiority (generally, the pre-colonial emperors of Vietnam didn't use their title in their relations with China). Claiming the title doesn't bring in any more money, or increase one's military power.