After getting back from a trip with a friend a few years ago, we swapped photos electronically only to find that the dates and times on our cameras didn't match up. Instead of our photos nicely meshing in the order we saw things, they were all over the place.
It only takes a few moments to reset the time on your camera for your destination and, if you sort by date like I do, it's a whole lot easier than manualling rearranging photo files when you get home. It's particularly important is you will end up photos from more than one camera. Make sure the date and time is correct.
Lesson learnt. Before taking my first photo in Cuba and the US last year I changed the dates on my camera.
Unfortunately, for my last trip I thought - it's only a three hour difference, I wont bother. Yep, that was a mistake. Any photos I took after 9pm sorted in with the next days photos. Annoying!
It also means that if I'm trying to remember something and refer back to the photos, I can't trust the time. Ok, yes I can work out the maths of subtracting 3 from the time on the photo but that's actually only true of Thailand. I went to Hong Kong before and after and that's only 2 hours behind home. And hang on a minute, was that adding time or subtracting it again? From time at home or Hong Kong? And what about daylight saving? I'm confused. :)
Change the date and time on your camera for match your destination. It's easy and saves hassles.