This property has effect only in virtual mode (when DataAccessMode is not Static). It is a performance tuning property. Do not change the default value unless you thoroughly understand the mechanics of virtual mode. The default value is 12%.

This property determines the distance (number of rows) to the end of a segment that is considered a 'danger zone', or a 'mandatory fetch zone', in the sense that the current segment must be changed to another segment (taken from the cache or fetched from the database) when the user positions on a row inside that zone. By default, it is 12% of 400 = 48 rows.

Reference

TableView Class
TableView Members