Virgin Australia does this on every B737 flight, all day, every day (except if there are no guests in business class).
On landing, once the front doors are disarmed and cross-checked, the second FA seated at the front (i.e. not the CS) will move to position themselves between the economy and business cabins, giving business class passengers the opportunity to get up and off the aircraft easily once the seat belt sign is turned off. (I believe they may also do this for weight and balance management relating to back door disembarkation as well, to ensure an even flow of economy passengers in both exit directions - so the aeroplane doesn't tip up.)
