FillFactor of a index
The fill factor of an index specifies the amount of space with is reserved for new entries in the index. A fill-factor of 80 for an index specifies that the file used for the index is fill for 80% so that when the user enters new data there is room for an new entry in the index.
In some situations, there are tables wich are not daily edited. An index with a higher fill-factor will save you disk-space.
If you specify a to high fill factor for a heavily edited table you will see performance loss and in the log you will see a lot of page-splits.
The page splits are caused by the fact that there is no room for a new entry in the index file and SQL will have to extend it.
Use proper fillfactor for Indexes: Very important to avoid Page Split. In general transactional table can be kept at 80-90 fillfactor.