Using keystone correction and lens shift to correct abnormal positioning and projection may be useful. However, they are some demerits associated with their uses.
Keystone correction does result in a reduction in resolution and quality of the image. This is due to the alteration in the image. Also, the more levels of keystone correction you use on a distorted image, the more obvious the degradation is and the more flaws it has. And there is a shrink in the number of pixels of the image the more clicks you apply on it. For example, a 1080p HD image can turn into 720p or lower, or ditto with 4K may be reduced to 1080p. Therefore, keystone correction should only be used when there is no other option in case the projector image is not parallel to the projector screen or wall.
As for lens shifting, the resolution and quality of the image are not really affected. However, it is more ideal to center the projector than to shift the lens off-center. Lens shift should be used if the projector is properly aligned with its wall or screen at a perpendicular angle. It becomes difficult to be used when the projector is at an odd angle with the screen, making the image to be less rectangular or square and more trapezoidal.