According to the Common Data Set for USC it is under “considered” but not “important” or “very Important”.
Typically with the amount of applications legacy doesn’t play much of a role anymore. Would come into play when it is between 2 candidates that match up closely and a decision needs to be made. Then typically the legacy would come into play. However, I guarantee if a legacy was a HUGE donor or famous it would certainly be “very important” for that candidate.