Its a very accurate tool, however its only as accurate as the data you put into it, if your muzzle velocity or pellet weight, zero range, incline etc is off then so will be the point of impact.
I use it as a shooting aide, it roughly tells me where the pellet should strike, you then have to apply your knowledge of the rifle your shooting and the environment your shooting in to make adjustments.
The most common errors are from the human side
ATB
Adam