Bonus wagering determine the quality and impact of a bonus. Numbers attached to a bonus say, 20X, means the multiplier or the number of times the bonus should be played to convert into a redeemable win.
This knowledge and information about these weighting is crucial, it is easier to be enticed by a bonus whereas without crucial knowledge of its weight it could mean wasting time.
If a bonus is capped on 4x, this means that one has to place four times the minimum amount to qualify for the bonus.
Conditions attached to a bonus also water down or improve bonus wagering, the less sringent, the more fun the bonus is.