Increasing the number of steps beyond what is needed for good query optimization can hurt Adaptive Server performance, largely due to the amount of space that is required to store and use the statistics. Increasing the number of steps:
Increases the disk storage space required for sysstatistics
Increases the cache space needed to read statistics during query optimization
Requires more I/O, if the number of steps is very large
During query optimization, histograms use space borrowed from the procedure cache. This space is released as soon as the query is optimized.