The fillfactor controls how full the index leaf pages are when an index is created or rebuilt:
The higher fillfactor the less space an index takes.
A value of 100 means the pages will be full and will take the least amount of storage space. This setting should be used only when there will be no changes to the data, for example, on a read-only table. A lower value leaves more empty space on the data pages, which reduces the need to split data pages as indexes grow but requires more storage space. This setting is more appropriate when there will be changes to the data in the table.
Change the default value of the fillfactor:
EXEC sp_configure -- show current settings EXEC sp_configure 'fill factor (%)', new_value -- set a new default value RECONFIGURE
Impact of a small fillfactor: