Sometimes people get into the habbit of playing overblows and overdraws with a lot of force. They feel that the overblows have to be kicked into action. They choke the blowreed and then push the drawreed into sounding.
There is no need for this, overblows and overdraws can be played with no more effort than is needed for a bend note or non bent note. The only thing that is needed is accuracy in resonating the right pitch.
Using a lot of force in overblowing is bad for the reeds it will damage the harmonica. Many beginning overblowers go through several harmonicas before they learn to play gently enough for the harmonica to survive.