Currently there's the attack button and the sneak attack button. It's very hard to tell if the conditions for a sneak attack are met (have advantage, ally is within 1.5m). The sneak attack button is available even when it shouldn't. Is the result a regular attack? Why not have only the attack button and if the conditions are met, add the sneak damage? Is there somewhere we can see the damage rolls, I'm never sure if the attack was a sneak attack or not.
I agree that the sneak attack button should only light up if the conditions are met. But for now you can hover over the enemy you're trying to attack, and if it says you have a bonus to hit from advantage (due to sneaking or height etc) then should tell you if you'll get sneak attack. You can see the damage rolls by hovering over the combat log text on the bottom right of the screen.
Honestly, I think Sneak Attack needs to be automated, not something you activate.
Eh, I think it's essential that we have the option to activate it. Sometimes you might want to sneak attack only on the second (i.e., off-hand) attack. Say you want to finish off a 1 hp enemy right next to you and then attack a 10hp enemy behind them. I don't want to waste my sneak attack on the 1hp enemy.