Here is my reasoning, I might be wrong, might be right :
If you brew a pale ale or lager at 3.8% alc and want to have it at 5%, it seems like adding sugar to up the alc content +1.2% would produce more nasties that could be tasted in the brew (by-products of fermentation) than if going with :
Option 2: adding a bit of 92-96% alc. to up the level to 5%, really won't take much and that alcohol is much purer than the 1.2% you'll get from fermenting sugar in your beer, would it be candi, invert or dextrose whatever… So, it should be cleaner in taste and very hard to detect : ferment a sugar wash to 1.2% clarify it and carbon filter it even, I doubt it would taste cleaner than water + 95% alc to make the alc content 1.2% It just makes total sense to me.
Unless that when adding sugar in a wort, when it ferments the things blend together and somewhat the sugar starts giving some good flavours like the malt/ and is totally different from adding some sugar wash to a beer. I highly doubt it.
and yes I know I could just add more malt, but I'm talking about adding 1.2% here, not much…