Intelligence or INT is used in those activities that require brainpower, like observation, all magic activities and also those manufacturing actions that are based on cult skills like creating certain types of weapons or potions. Biochemistry is a very important production skill that is based on INT. If you want to run a pharmacy you need as much INT as you can get. INT is also a good skill to have for prostitutes since it may help evade a prostitution crime if her observation skill is also high. Dumb prostitutes will get caught more often than smart ones. The same is true for officeholder who illegally destroy crime-files to protect friends from prosecution or perhaps as result of a bribe.
In general, magic users, pharmacist, doctors and certain types of criminals can make good use of high INT.
If you intend to build your character up to become a demon, INT is also a good idea since demons are high level cultists and must be able to make use of INT for many reasons.
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