To remove from view any effort assignments that have zero demand in the interval of the Get Data, select Tools > Options. In the Zero Demand Options area of the dialog box, check the “Hide zero demand on Effort Forecasts” box, and click Ok. The zero demand assignments are no longer visible. The assignments have NOT been inactivated or deleted, the rows have been hidden. These “hide” options can be removed by the Options dialog or by the Filter > Reset Filter Options menu command.
Similar options are available to hide zero demand on Project and Resource sheets.