be aware that SGI maps back to the physical dimensions of you environment. if you are in a large spaces where reflections can come back at substantial power and time delay >350 ns then SGI should not be used. for reference radio waves propagate at about 1ft/ns. the system won't break but the radios will try packets that use SGI and they will fail causing un necessary re transmits
SGI should never be used outdoors and large spaces like gymnasiums that are using APs with standard internal antennas SGI should probably be turned off.