The voltage is pretty critical, the age old YB issue we see is at high RPM with lots of boost the Turbo is at its hottest, cooking the Alternator. This is the same time you are demanding optimum fuel delivery, fuel pump voltage, injector speed, coil voltage, so things go bad quite quickly.

I aim to keep the ECU at 14-14.2 under all driving conditions, so coil voltages, injector speed etc remains stable. I commonly see ECU voltage down to under 11v!

If you have 22ms to open and close and injector its critical they remain at optimum voltage for speed, so the injector open time can be optimised, especially on something with fuel limited tunes like T34 803s.

The load site issue isnt really a problem, it just means the map needs a little work, modern fans etc draw less current so the load on the engine is less, so can stop the issue, but the lean load cell still exists, just doesn't get referenced. If the load cells referenced are AFR stable compared to idle you wouldn't even notice the jump in sites.
Cars that are leaner at idle suffer more from moving load cells under slight load than those that are richer.

When we started doing the Alternator to battery cables, we were finding even the Electric windows were operating faster, so its crazy really on the effect it has on the whole car to optimise the battery voltage, after 30 years the wiring is not in good order on most.