Set 3d cursor & origin – Blender 2.8 quicktip
25games writes:
Hey Pixels,
Working with the origin and the 3d cursor could be a powerful tool. It is very useful for game production and working with modifiers and it is as well very helpful for rotating your object beginning on a certain point. In this Blender quicktip tutorial I will talk about those functions for Blender 2.8 and 2.79 (shortcuts).Cheers

useless :)