I'm basing this off what I've seen several times, typically from the most senior captains. PF is assigned altitude like 3000. Re-cruises the box. Airport in sight, cleared for visual. PF hits direct to the last point prior to runway and says, "We're visual, setting tdze (or zeros). PF hits altitude intervene and vnav goes into descent mode and immediately sets FUM speed. PF says, why'd it so that? So he hits speed intervene and dials 250 knots. Airplane goes into idle descent mode.