Well firstly airstarting is really a high power kind of thing so isn't used in low power, I'm guessing that you want to do it with LPR motors since this is in the LPR forum!
I think (but I'm not too sure so don't quote me on this) that electronics are used to time a ceratin interval from lift off and then the motor is inginted using an onboard power supply, this means lots of weight which can't be lifted by LPR motors. I beleive that people use it to get higher altitude, a larger motor is ignited first to get the rocket moving and then other (usually smaller) motors are ignited in the air so their thrust isn't used in getting the rocket moving, I'm sure there are other reasons too though.
The standard method of staging (ie booster motor sends hot particles to upper motor) is kind of airstarting, the motor isn't ignited on the pad.
I'm sure others will chime in, HTH.