Spot brick pointing or the whole wall
If the worn joints sit in one area, like under a downspout, repointing just that section usually makes sense, and we'll work to match the old mortar's color. When wear runs across the whole face, patching ends up chasing it, so I'd redo the wall at once. What I won't do is surface grouting, a thin mortar wash smeared over the joints, because it can't do repointing's job, and the National Park Service's guidance for historic masonry recommends against it.

