Totally a personal preference based on your assessment of benefits vs. liabilities for your situation. I'll say only that it's a lot easier to put the card in before you mount the camera, than to do it later after changing your mind.
Ok so it think I get this out of it:
Its like insurance but cheaper
SD cards are cheap.
Provide some fault tolerance in Disaster recovery.
No immediate drawbacks
Other than might not be worth it on preexisting cams without them.
Put in place on first maintenance.
If you use an SD card, you should also only set the SD cards to record on motion.
They really get wonky quick if recording 24/7. It is well documented here that most cameras do not do well with 24/7 recording to SD cards.
In most instances when the SD card fails, it simply quits recording to the card, and there have been a few instances of the camera rebooting.
If the camera is a hard to get to location, many times a reformat buys you time (maybe days or years), but you can also hit the "hot swap" button in the GUI and it will then ignore the card until you replace it.
I don't consider it that big of a deal for the extra redundancy.
It is on every camera I have that has an SD card as it allows you to remove the SD card without powering down the camera and not corrupt the card or cause the camera to spaz out removing memory while it is writing to it.