What are the situations in which it is recommended to say "Bismillah" and those in which it is not?

It is from the Sunnah for the speaker or preacher to begin by praising Allah. When reciting the Qur'an, seeking refuge (isti'adha) and saying "Bismillah" (basmala) are prescribed. Some scholars have divided the actions of people into three categories concerning the basmala: those in which it is prescribed, those in which it is not prescribed, and those in which it is disliked.

The first category: such as ghusl, wudu', tayammum, sacrificing an animal, reciting the Qur'an, eating, drinking, sexual intercourse, riding an animal or a ship, entering and leaving the home, entering and leaving the mosque, when putting on and taking off clothes, when closing and opening doors, when turning off and lighting lamps, and during permissible sexual intercourse.

The second category: such as prayers, the adhan, Hajj and Umrah, adhkar (remembrances of Allah), and supplication (du'a).

The third category: such as forbidden and disliked acts, because the purpose of saying "Bismillah" is to obtain blessings, and forbidden acts are not intended to be multiplied.