There are betting sites like that, even most betting site are having such feature now because they are using it to make profit.
Assuming you take club A to win club B with $10, 2 odds. That means your profit is $20 if you win.
If the match has started and they are playing draw, the $10 you stake will be reducing drastically as the match continue with draw or the other team is winning, or you can cash out if you think the match can end draw or club B would win.
If club B score 1 goal, the amount you want to cash out will reduce to the amount you do not like, and the more the match goes on, the money will be reducing.
It can get to a point the cash out will no more be available.
Cash out will still be in a way the person would have been losing some amount or would no more be available.
I will advice you to just take gambling as fun and play your game as fun, anything can happen. I have long time not going for cash out again, I use it when I was addicted to gambling unlike now. I take a club or team to win and I do not care if anything happens as I use the amount I can afford to lose.
My profits had been reduced countless of time because of this feature because me having fear of lossing big on bets.