Repointing a few joints or the whole wall
If the bad mortar is in patches, say around a downspout or along the base, I'd repoint those joints and leave the sound ones alone, because tight original joints still do their job. When most of the joints across a wall have worn back, a full repoint makes more sense than chasing patches. If the bricks themselves are cracked, or cracks step across the wall, the joints aren't the whole story, so we'd look at foundation repair before filling them.

