RockStar2005
Headphoneus Supremus
Keep it disabled.
Enabled with "Flat" sounds the same but the EQ it's still in the processing chain which adds a load to your phone's resources.
"Flat" is there to quickly compare between some EQ curves and none.
Oh Pooj is right. I totally forgot.......turning any EQ on will ultimately use up more battery power. So if you just want Flat, better to leave it off.