As an automotive electrical design guy ..... my thoughts on the so-called "big 3".
1) It basically does no harm.
2) It provides little or no benefit for most vehicles.
3) If you have some massive electrical loads like boombox stereos or massive lighting, it may have some benefit, but you better upgrade your alternator and battery and regulator as well.
4) You can get 90% of the benefit just by optimizing your existing connections, cleaning them - the ground, battery posts, and starter terminals. Add protectant and torque them properly.
5) If you are having electrical demons, this is no cure. All this does is reduce -- by a TINY amount -- the voltage drop across your cabling
.
I'd love to hear success stories from someone who has done this. But don't tell me it feels better because you spent a bunch of money doing it
.