When shoulder firing a rifle, yes, cheek weld is important because it has to be the exact same every time for the best accuracy.
I will relate it to your situation. If instead of backing off of your rifle after sighting the target, if you were to keep your cheek on the gun you would slightly change the harmonics of the gun, and yes, the shot would be out of the group. It is important. For you, the importance of cheek weld is to not have it... odd, but still a consistent cheek weld (or lack thereof) is what you are doing.