Always format in-cam, pretty much standard advice. It's just that some cams can only format FAT32 so if the card starts as exfat, the cam can't handle it, so you change the card format on your computer first, then the cam will do a formatting in the way it prefers.
Mobius and G1Wc both worked on FAT32, but neither cam could format a card taken from the other cam, even with all the accessible files erased. To resolve this so that one spare card would work and format inside either cam, I first formatted the card on the PC using sdformatter since the windows-supplied junk couldn't, and then it would format inside either cam afterward. That has something to do with the hidden files on the small 'reserved' section of SD cards and is a common problem when switching cards between almost all cams.
Phil