First of all, studying the emperor is to study how to be an emperor. What's the use of this research? Help the country's supreme ruler to do his job well, let the country's supreme ruler identify the dangers around him, know what to do and what not to do, and let her distinguish whether people around her are good or bad and how to use her power.
In a word, this theory is a very useful book for the emperor. Since childhood, emperors of all dynasties have asked to read books about the study of emperors and kings in addition to reciting the four books and five classics. Therefore, the study of the emperor became popular among the ruling class, but many officials and ordinary scholars did not understand it.
For example, some emperors have a lot of traitors around them, and loyal ministers always want to get rid of them, but the emperors try their best to protect them and sometimes even excuse them. Why? Doesn't he know that those people are traitors? He knows that this is a check and balance in the study of emperors.
For another example, civil servants and military commanders are not allowed to marry. If civil servants gradually gain power in the court and military commanders gradually decline, then the emperor will definitely suppress civil servants and promote military commanders.
The study of emperors also told the emperor that ministers can form a party, but not everyone can form a party, such as the Eight Kings Party in Yongzheng period, which is too big and must be suppressed.
The emperor hoped that several political parties would fight against each other. For example, during the Qianlong period, four military ministers, A Gui, Liu Yong, Ji Xiaolan and Li Shiyao, were United, and he had to promote Yu Minzhong and Xiao Shenyang, whom they didn't like, and suppress them. This is to balance power, so that the emperor can sit firmly, and there can be no powerful ministers in the court.
In short, the study of emperors teaches emperors how to be a good emperor, and there are many contents about checks and balances.