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This discharges any capacitors / memory within the ECU and around the car so ensures all memory settings are wiped clear - back to the factory default.
This will reset all the systems on the car and you may need the radio security code to get it going again, and ensure that the keys are in your hand when you re-connect the battery as the car may lock and turn on the alarm
however if the light does then blink on again you're going g to need a garage visit to get the fault code as it could be anything from a faulty door switch to a faulty airbag squib