In SNES

I recently downloaded the NES ROM and was checking the game out.
I got hang of the controls, but one thing that bothers me is, the button which causes butthead to poke his nose or slap beavis.

Is this only for pure entertainment, or the feature may come handy during game play?

That feature is purely entertainment, and will not come in handy during the gameplay. At least not that I know of, because I've played the game through and I have never really had to use it for anything.