`莅临` is strictly formal. You would never use it with friends, family, or in casual conversation. It is almost always used by a host or a subordinate to describe the arrival of a guest or superior.
Welcoming Speeches and Banners: This is one of the most common uses. Banners and opening remarks at events frequently use this term.
Formal Invitations: The term is often used on written invitations for conferences, ceremonies, and grand openings to show respect to the invitees.
Official News and Media: News reports about government officials, foreign dignitaries, or famous experts visiting a location will use `莅临`.