Halachah: Reciting Hallel on Yom Tov.
Minhag: Reciting Hallel on Rosh Chodesh.
Chumrah: Reciting Hallel in synagogue on the first two nights of Pesach in case you won’t say it at the seder. (Rema opposes this.)
Stus: Refusing to help your wife clean up because you have to recite Hallel at the seder while being totally oblivious to the fact that she, too, is chayev in Hallel at the seder.