Excel fro mac and PC

I am running excel in a multi platform environment (PC
and MAC) I have found when you update a file on the PC
side, and then move it to a Mac and try to view it you
need to open in excel first and re save the file in the
format you want. Seems strange that you save the file on
the PC side in a format and need to open on the Mac side
with excel and save it with the same formatting as you did
on the PC side. Duplicating your work???? is their a
setting in excel (most likely on the PC version) that
needs to be turned on or configured? This would be
helpful.
Thank you in advance.