For one, electrolytic capacitors can have pretty large tolerance for their initial value. The question then is also whether a fresh cap’s value is closer or fur

For one, electrolytic capacitors can have pretty large tolerance for their initial value. The question then is also whether a fresh cap’s value is closer or further away from the value the old cap initially had compared to what it drifted to. More generally however, you just don’t need to replace a capacitor in something that works well and that is not anticipated to break catastrophically because of the capacitor plague. If the caps do eventually drift off so far that it affects operation, replace it then, and then it makes sense to take the opportunity to replace others as well as precautionary measure. Sometimes you know that a non-plague cap will likely fail because it’s right next to a massive heat source, and you may replace it early with good reason. But sometimes I see people literally replacing 80 caps or more without reason, when I have the same device sitting at home with its original caps, still doing its job well within spec for years.