I'm curious how some people decide that they don't need to touch the truss rod when switching strings....?
Do you just just go by feel and general observation....or do you actually use a feeler gauge and *measure* the change in distance between the frets/neck and the string at the same mid-point position of the neck, when changing string gauges.....?
The thing about truss rod tension....there is no one exact number, so it could be anything say, from 0.2mm to 0.5mm for an electric guitar....but for a given guitar and your preferences, there will be an optimal number that you would want to maintain when changing string gauge...and without a feeler gauge or other precise way of measuring, it ends up being just guesstimating.
Of course....if the "optimal" number for your guitar is off by 0.1mm or 0.2mm, you may not be obviously bothered by it when playing, and therefore you assume that there is no need to adjust the truss rod...but that doesn't mean that string gauge changes have no effect or that you don't need to readjust the truss rod and maintain your optimal number, which gives the best feel/play.
I've always adjusted the truss rod when I switched gauges...and there WAS always a small change in that fret/neck-to-string height in the bow of the neck when I switched gauges.
Going from light to heavier didn't seem as problematic, though enough of a change could cause intonation problems if th neck bowed more significantly....but if you go from heavier to lighter, the neck could go flatter and therefore cause more fret buzz in the upper/lower portions of the neck.
It does depend on the guitar/wood too....some react more, some less to minor tension changes....which is why a feeler gauge is an easy/precise way to check. I have a small blade feeler gauge from back in the days when car tune-ups and spark plug changes/adjustments where more common. These days, you go for over 100k miles and not need one....so that feeler gauge found a home in my guitar tool box several years ago, and it has just the right choice of feeler sizes for guitar work.
Hey...if you're happy with the guitar action/intonation regardless of any string gauge changes, and you don't want to be bothered checking it with feeler gauges and doing all that micro-adjusting....then leave it alone.