Gone are the lovely, thin, white joints, to be replaced by ugly, fat, grey, cement ones, with splashes and splosh marks all over the face, ground and surrounding parish. Not only does it look appalling, but Portland cement is very, very hard, and will damage the lovely soft clay of the original brickwork. After several years of frost and rain, the wall ends up like this:
Almost gone, thanks to bad pointing. What a (expensive) shame.
Always best to use the right mortar!