I agree with the other responses that it’s a bad idea, and might not even have the effect you want. If you’re having a session 0, and you should, that’s the time to discuss what kind of game you want to run, and also make sure the players are on board. There’s plenty of ways to encourage more role playing.
And getting into crazy cinematic detail for all of combat can really slow down the game and limit other rp opportunities. If someone is going off on their attack on goblin 4 of 8 and doing 2 damage or something that would get old quick. But if it’s a long hard fought battle against a mini boss and there was great teamwork and they rally and maybe a pc hits for 10 damage and the big bad only had 11hp left and no minions left, fudge it a little and ask them how the killing blow landed. If they’re new, you can do the description the first time or two and edge them along.
Or if a pc has been doing some great rp there’s always loot to reward them, if they use a rapier and the loot lists a +1 longsword, switch it up. There’s so many ways to reward them, I don’t think telling them a mechanical benefit will help, I think it’d just get cheesy and abused. I think a little more subtle nudging in the right direction.