Please help me to understand. I'm having hard time to understand the difference between Geometry & Work offset(G54) and their application in Fanuc Lathes.

If I touch off part face (Z) and set G54 Z0 [MEASURE] do I need to set Geometry offset Z0 [MEASURE] too? Why two different offset in same machine for same Z touch off? Please help me to understand their difference in application.