IMO, the biggest danger in relieving the pressure is if the water is still hot. We don't travel with the WH on, so I just drain it in the driveway when I get home. I know the heater hasn't been on in a long time, and the water is no longer hot. So I lift the valve (and open the HW faucets) and that relieves all the pressure. Then I pull the plug. When all the water is out, I close the valve and replace the plug. Just make sure you're not hooked up to water and your pump is off or it'll try to refill the tank. Be careful to stand aside when you lift the pressure relief valve if the water is still hot, but the procedure still stands, you just have to be more careful; you could get burned.
2014 Jay Flight 28 BHBE
2015 RAM 2500 6.4L HEMI, Tradesman 4x4, 3.73
Blue Ox SwayPro (BXW 1503)
Upgraded from an REI internal frame backpack and a Eureka 1/2 dome tent!