I transitioned from legacy to current. Ain't no thing
When I tried to play WC3 Dota a few years ago, the hardest thing about it was the awkward positioning of hotkeys for some heroes. I didn't really have a problem memorizing the keys, but pressing them was kind of weird. Sometimes I would try to hit what I was used to in Dota 2.
Going T -> R -> D with Pudge was really awkward for me.
Honestly I haven't really understood why some people prefer to have it on. I mean I guess now it's viable if that's what you prefer, but I have never really understood the logic behind it. The only thing I can think of is trying to not lose the chase on someone that's going in and out of vision, but this is mitigated by A+Clicking.
Before they fixed it though, there used to be no good reason to leave autoattack on in Dota 2 (Source 1) when you had stuff like Centaur's Return and Enchantress's Untouchable proccing on initiated on attacks and not when the attack connected.
There was a Fails of the Week clip a long time ago where an NP was on the cliff and a Centaur Warrunner was right below him. The NP had autoattack on and he kept hitting S to cancel attacking, however Return procced on initiated attacks, so he was just fucking himself over with every cancelled attack.