The default FILLFACTOR is 100 and I have been told at times to reduce it to 80 or lower so that page splits will be reduced due to the empty space on each page.
I don't understand this--if a new index is created on a table with a default FILLFACTOR of 80, 20% space of each page is left empty. So assume a row needs to use 10% of a page, so when it's full it can hold 10 records. With a FILLFACTOR of 80, now it can only hold 8 records. So when you add the 9th record, will there be a page split? With 100% FILLFACTOR, a page split will only happen on the 11th record, so it seems that a lower fill factor makes it worse.