When you log in to your account you usually see a yellow number next to your wallet if you have a bonus awaiting. I sometimes just accept the bonuses just to get this symbol removed. It's just a cosmetic thing but perhaps it would be good thing to be able cancel the bonus offered instead of being just able to cancel a bonus accepted. So for now I've done it so that I accept the bonus and cancel it to get rid of the symbol.
Yesterday I ran to a funny problem with this. I had a deposit bonus I had used and had a ~10€ bet left from that, had 3 bets right out of 4 in the parlay and the last one was failing in the end of the game so I canceled the bonus. I accepted a new bonus that I had no intention of using just to remove the yellow number from the screen, but I could not remove the bonus (I still can't). This was also perhaps the reason that I could not get the free spins from friday happy hours 19cet - 21cet as I had an active bonus on the account. No problem with not being able to play the free spins, just wanted to report this that has been on my mind and caused some extra job for me and yes it originates only from a cosmetic problem.