 When the input contains several keys that are close to each other (clustering), those elements are likely to be placed in the same bucket, which results in some buckets containing more elements than average.The worst-case scenario occurs when all the elements are placed in a single bucket.The overall performance would then be dominated by the algorithm used to sort each bucket, which is typically formula_1 insertion sort, making bucket sort less optimal than formula_2 comparison sort algorithms like Quicksort.