For cars, toe-in is for rear wheel drive; toe-out is for front wheel and all wheel drive. RWD has the front wheels drag the wheels straight; the power on a FWD AWD front wheels drives them froward. The idea with toe-in/ toe-out is when the wheels move the reaction will straighten the track. On race cars, toe out is sometimes used to make a solid axel RWD car oversteer some to counteract the natural understeer of a front engine RWD. Toe-in/out on a full size airplane depends on how it reacts one wheel on the ground while the other is in the air. Crosswind landing control is what they are after most end up with toe in. We dont have the ability to sit in the plane so models go with what dampens the most.