The bonus is part of the feedback mechanism between the treasury and the decentralized global reserve bank concept. This is a separate mechanism from the mining/validator rewards (i.e. minting new coins). The bonus is paid out to mining/validator nodes during various activities, for example when a node joins a new parallel chain. To reduce currency in circulation, the bonus can be reduced to zero, and the associated currency burned instead of paid as a bonus, governed algorithmically. This provides an incremental, controlled means of managing the currency in circulation, without necessarily changing the minting rewards for block production.
The DGB monetary policy, in general, is focused on managing the currency in circulation to reduce price shocks with economic activity creating a more stabilized currency suitable for exchange of value.