Choosing a value for reservepagegap depends on:
Whether the table has a clustered index,
The rate of inserts to the table,
The number of forwarded rows that occur in the table, and
How often you re-create the clustered index or run the reorg rebuild command.
When reservepagegap is configured correctly, enough pages are left for allocation of new pages to tables and indexes so that the cluster ratios for the table, clustered index, and nonclustered leaf-level pages remain high during the intervals between regular index maintenance tasks.