in the 90+% of cases where you'd want to sneak attack on your first (possibly only) attack each turn
I certainly dont recoment such approach to anything ...
Just remember how well it worked for Reactions (Hellish rebuke for example) ... Larian also thought that we would "
in 90+% of cases want to..."
Surprise! Surprise! We dont.
In the remaining cases, it's almost a certainty that you'd want to sneak attack on your 2nd attack, so it's still only a total of 1 extra click.
In case when you have 1 extra oponent ...
What if you have 20 of them? (Goblin camp)

See, this isnt really matter of amount of clicks ... its just that its anoying extra action you dont want to do ... same as when you want toggle, rather than active skill ... its not like that pressing that button is somehow hard, long, or w/e ... its that you dont want to press it, that is what anoys you. :P
And it goes same other way ... one of us will be pissed in the end, its inevidable.
That's the great thing about the toggle system over Larian's automatic reaction system though:
It still allows full player control. Which is different from how Hellish Rebuke works: not giving players the real-time decision to use it or not.
If you have 20 extra goblins, you still will still be limited by the # of attacks you have per turn. For rogues, this is 1 bonus action attack by default, 2 if you're a Thief. So 3 or 20 goblins is effectively the same amount. And it's an even lower probability that a player would need to make their first two attacks non-sneak, and then the third attack a sneak attack.
And there's still the huge positive that, with a toggle, you can combine sneak attack with other weapon/class/race attack abilities. And sneak attack on opportunity attacks.
I shouldn't have been so categorical; your explanation makes sense. In case a 1 hp foe is standing next to the rogue, that is quite helpful (I'm not being sarcastic, it happens more than I thought it might).
A few counterpoints:
1. The current system already has this benefit (or very close to it). If you're worried about wasting your sneak attack on a low hp enemy, just start off with your off hand attack. I'm almost certain that this maximizes expected damage anyway, so the toggle doesn't present a strategic edge in that regard.
2. It would be the only opt-out toggle... Wait, that's not true. Bardic Inspiration is mostly off/partly on. And I couldn't say whether Great Weapon Master is on or off by default.
3. Speaking of GWM, a toggle would be compatible with attacks of opportunity; the current system isn't.
...
Ok, I can see how a Sneak Attack toggle could work. However, I'm not a fan of the toggle system working in quirky, inconsistent ways. Sneak Attack would be the only toggle to switch positions without direct player input. Given how diligent Larian are about explaining their game systems, that might be too ambitious.
Best to resverve judgement for patch 9. Just four weeks to go...
All good points, especially about different toggles working in inconsistent ways. The main mechanical difference between my suggested toggle is the fact that it
automatically turns back on after a single attack with it off, whereas other toggles stay off until you turn them back on. I believe most toggles default to on, so it'd be consistent in that regard.
At the very least, Larian would need to make sure that BG3 tooltips sufficiently explain how each individual toggle works - maybe color code them to indicate their differences?