I am asking this question to evoke a list of situations in which one's personal feelings, intuitions, beliefs, and/or tastes have a role in creating the halacha.
I can think of a few on my own. With food, it is quite frequent; according to some opinions, one makes a bracha first on the food one likes most. One may arguably omit meat or fish or other traditional foods Shabbos if (and only if) one doesn't like them. And it seems there are many issues connected with subjectivity in hilchos Shabbos v'Tom Tov, in general: איסטניס; ochel nefesh; whether, based on your personal standard of acceptability, you are allowed to improve something further; etc., etc.
Apart from food and Shabbos, it is a bit harder to find examples. Shidduchim--and the necessity of seeing a potential bride, and choosing her based at least somewhat on one's own tastes--come to mind. In this arena, one's personal יש--that which makes him himself rather than another Yid with the same status--is ascribed some sort of religious legitimacy.
There were also nedoves, freewill offerings, which we also have in tefilla today. And finally, I once read an opinion that the decision of whether to say hamapil before or after other bedtime prayers should be based on one's personal sense of what to do.
Can anyone point out other significant or interesting points of halacha where the individual judgment of a layperson determines the law? (I ask about personal rather than communal or interpersonal preference/identity. And I am asking mostly about halachos--but opinions of the greats on the importance of individuality would also be very interesting to hear.)
Bli neder, sources later