This parameter indicates whether sorting of index keys will occur during index creation. Performance of index creation is enhanced by performing a sort first, particularly for indexes with low cluster ratios or cluster factors. Performance of queries can also be better if indexes are created with a sort. The cost of this performance enhancement is the increased disk space required for the sort, which could require twice the amount of space as creating an index without performing an initial sort.
Recommendation: Use the default setting ("Yes"), unless you do not have enough disk space. Note that the disk space required for this sort is approximately equal to the amount of space needed to SELECT the columns of the index from the table with an ORDER BY clause on those columns.
If you have a symmetric multiprocessor (SMP) environment and specify "No" for this parameter, the multiple processing that is possible in an SMP environment is not used during index creation.