OTS= general, basic, safe map used and able to run on any car with the exact mods listed by the company. There is always room for improvement over these "generic" maps, but they are also far better than not having one at all.
MAF= Mass Air Flow Sensor. Used to calculate/calibrate with your a/f ratio so car doenst run lean/rich.
Certain intakes especially CAI have the wrong diameter or a bend that causes turbulence and it throughs off your MAF, then making your car run poorly. Maybe not right away, but eventually it can/will.
"2007 WRX- PPG'd, 20G- Tim Bailey tuned
Stage 2 2005 WRX