As the unit is digital you're zeroing out the electronics too. Battery condition, temperature, amount of vibration it was subjected to since last use and a host of other things can effect it's starting (power up zero) point. If you want accuracy I'd do it. If for no other reason than to take one more thing out of the list of possible reasons you might end up chasing your tail around looking for a ghost problem that doesn't exist. Just Sayin.
Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.