I don't put it anywhere I want; I mark where it should be for convenience.

I balance my airplanes at 30% mac with the wing on, and then remove the wing. I then see where the fuselage is balanced and then mark that place.

Why? So I can check the fuselage CG in the event some of the internal components get moved around, or a fuselage mod was made, or I need to deviate from the 30%mac.