I've used both shrink tubing and Sugru on iPhone cables. On the MacBook charger, just Sugru. Both will fail eventually. I find that typical shrink wrap is too stiff and creates stress riser. After a couple of years, my cables are more patch than original.
I'm planning on doing this with shrink wrap. My plan will be to not completely shrink the cable-side of the shrink wrap to leave some play so I don't create a stiff point.
I have tried using Sugru to fix my Mac charger. It only worked as a temporary fix for me. I think the problem is that Sugru is not elastic enough and tends to crack when it bends.