It would really help people like me, besides there's already a submit button on the phone. I bet it's there in case your phone messes up, but the game tends to drop my pieces prematurely when I drag them anyway (which accounts for a few of my losses).
Look, it just helps me visualize the game better. Besides, premove doesn't even exist in actual chess, since when should there be a touch-move rule online? That's like if you click on a piece you have to move it, and that would be stupid.
One thing I absolutely love about the Chess.com phone app and online chess is that nifty submit button. It lets you visualize what your move would look like before you make it. Often times I calculate my moves, then I would impusively make them before making a last-minute review. The submit button lets me see if that move was a mistake, and prevents me from giving away a piece by accident. That's why many games I win end up being games played from the phone app. I've even played a game on my phone, was on the verge of winning, then switched to the computer and lost.
The submit button has to be implemented into live chess. It would be, of course, an option, like premove. You'd want to turn it off for blitz/rapid/lightning, or it could be off by default for those types. But there has to be some sort of a submit button, which would be especially useful for 30 minute and 15|10 standard game types. If there was a submit button, I'd win much more often.