If for any reason, one of the countries you have visited claims that you did not re-export some or all of your equipment, they can make a claim for the import duty to be paid. Money to cover any possible claim has to be lodged with the carnet issuer in advance in the form of a bank guarantee or cash or they may have their own indemnity scheme. The amount of this security will be based on the values declared on the carnet, the type of the equipment, the length of your trip and the countries you are visiting. The carnet issuer will let you know how much this will be.