The defenders might decide to throw one, cheaper element of a contract, in order to focus on the more valuable element of the contract, in order to ensure that the overall game is not profitable for the declarer.
Similarly, if the defenders detect that the declarer has overbid (as in Overbidding), they can kontra the element that the declarer isn’t pursuing.
If the declarer has overbid a contract (as in Overbidding), they need to watch out for silent bonuses that the defenders could score on the less-valuable parts of the contract. For instance, if the declarer pursues an ulti at the expense of the parti, and defenders make the 100 bonus as a result, the declarer will pay more for the component they won.