Page splits are expensive operations. In addition to the actual work of moving rows, allocating pages, and logging the operations, the cost is increased by updating:
The clustered index itself
Page pointers on adjacent pages to maintain page linkage
All nonclustered index entries that point to the rows affected by the split
When you create a clustered index for a table that will grow over time, you may want to use fillfactor to leave room on data pages and index pages. This reduces the number of page splits for a time.
