This property determines whether the band will always be the exact size you specified, or whether you want to allow the band to increase or decrease as necessary. The two options are phStatic (always print the same height) and phDynamic (print the height needed). Generally you will leave this as phStatic unless you have TppRegions in your band that may or may not print. In that case you would probably want this to be phDynamic so that you don't have a large blank area.
NOTE: If you have TppSubReports that are part of the band you can still make this phStatic. The SubReports each have their own band that controls how they print.