Where do cables upgrades have the most impact?

teo_audio’s post should be a separate starter of a thread! Particularly the ’Compensating for NOT neutral equipment" (my words his idea).In fact I am starting a thread about it. So please do not add more about it here.It will have my name on it but I give credit to teo.
Here is the link to the new post on teo’s topic: https://forum.audiogon.com/discussions/problem-of-compensating-with-cable-a-component-tone-problem

Decide IN ADVANCE how much money you want to spend. Find a cable you might want to try. Get it long enough to fit anywhere. (usually 5 feet or 1.5 meters is what I like) burn it in from the CD player...Since that is the strongest (highest level) signal. Then try it all over the system. Where it sounds the best, well, that is where it should stay.
Or, instead of just buying a cable, borrowing cables from "The Cable Company" those are already broken in. So you can try them all over right off. If they impress you , buy one. If not, send it back, try another.
You DO pay to use them, but if you buy ANY cable, the rent money you paid is 100% credit to purchase.
I am not silly enough to recommend ANY cable LOL.

For the impact of aftermarket power cables, The wall or conditioner.. Does not matter. Power cords can be effective from/to either. Plus consider the wall AC duplex in this equation. The AC duplex can also have an effect on the sound (specially if aftermarket powercords are used)

The one problem with "Shorter is better" is down the road, when you move stuff around, or change racks, or buy a different gizmo. Suddenly your once just right interconnect is discovered to be three inches too short??? (the old box RCA were on the left, now they are far over on the right...)  I long ago used to believe in the just long enough IC. And over the years I have gone the total opposite. NOW, all my newer IC are 1.5 meters long. Long enough I am not going to have to worry about 'TOO SHORT $&@!!$(# !" anymore. And those are $1,100 a pop IC.                           
Just a shout out for buying a definitely longer than just enough when you buy big money cabling. For good reason, a little LONGER is, in the long run (pun intended), better. (primarily for your wallet, and I being a spendthrift cheapskate, watch that carefully)     
On the other hand, if you buy cheap cables, it hardly matters, Or if you change cabling like some folks change clothes. no problem.

The ’industry’ exists because someone who BUYS cables wanted something better. One ’better’ cable at a time... It grew. If no audiophile bought them, the industry would not exist. One actual plus for consumers is cables generally do not wear out. I still have cables that I made in the 1980’s. So aside from wanting better... no need to ever buy more. Cable company advertising is only to lure you away from SOME OTHER CABLE COMPANY. No one walking down the street accidentally saw a cable company advert and decided Gee I must NEED those bad, and rushed to buy some.
I am probably like a lot of audiophiles in having a pile of cables I do not use anymore. All told between IC, PC, speaker plus video or digital I must own thirty cables not in use, sitting in the closet. (anyone need a Monster S-VHS cable??? I only keep one because.. never know I might suddenly want to use it.. for????)   
As for "the most".. Priorities. Sometimes you might be best off spending your money on some other audio doodad. But sooner or later you might, maybe, decide to spend that $3000 sitting around on a cable? Who knows.. I did. (and glad I did)