From chuqui over at photos.stackexchange.com on How often should I format my memory card?:
I format my card every time I stick it
in my camera and start a shoot.
I do this for a couple of reasons.
First, it means every time I start a
shoot, I don't accidentally leave the
previous shoot on it (and it also
means I don't delete it until I start
the next shoot, by which time those
images are safely on various backup
disks; gives me an emergency backup on
the card until I'm sure I've got
multiple copies elsewhere).
Second, I use multiple camera bodies,
and I know people who've had
corruption issues with cards formatted
by the computer (which I never do) or
by one body and used in another
because the bodies interact with the
card slightly differently. By
formatting every time, I know the
formatting is what the camera wants
and is expecting.
Third, formatting at the start of the
shoot will (or should!) catch a card
that is starting to fail. At the
least, it'll catch some early failure
modes in the card -- and in two cases
for me so far, it has. So if the card
hits an error during format, I know to
immediately retire it. I'd rather find
out I have a card error at the START
of the shoot that midway into it, or
worse, when I'm trying to read the
images out later.
Note: any time I get a card error, I
retire that card. Cards are cheap.
Dead cards that eat my only copy of an
image is expensive. And formatting a
card every time means that every time
I shoot gives me a blank slate in a
known state that hasn't reported an
error. Which means many fewer
potential problems later. And FWIW, I
basically never run into corrupted
cards, lost images or problems during
a shoot or during a post-shoot import.
Even if it means the card will wear
out sooner, I don't care. I want
reliable cards, not ancient ones. I'll
happily replace them rather than try
to recover images from them....