Every component that is replaced, increases the potential margin for error
by the person replacing it. I have had many items cross my bench over the
years, which have been 'elsewhere' first, and have seen wrong values
fitted,
caps in backwards, diodes in backwards, damaged print and so on, amongst
the
many components that have have obviously been shotgunned, as evidenced by
the flux all over their joints. I have also seen unsuitable substitutes
fitted, where technicians have had insufficient understanding of the
requirements of a circuit's design, and have just put in 'what came to
hand'
in order to complete their shotgun.

Yes, but you and I don't make such mistakes.