MVT Digital Direct Peugeot 103 electronic racing variable ignition

Inner rotor MVT DIGITAL DIRECT, with light, electronic Peugeot 103

what is variable advance and what is achieved by being variable?
When the engine is at low revs, it is ideal that the degree of ignition advance is greater, i.e. that the spark jump is further forward than when the engine is revving at full throttle, whose spark jump should occur closer to PMS (top dead centre) to extract the maximum power from the engine and have a more usable spark curve.