Traditionally-cooked steaks need to rest. That is, they need to be placed aside for five to ten minutes before cutting and serving. This resting period is to allow time for the temperature gradient within the steak to even out. The cooler center is gently heated by the hotter outer edges, while they in turn lose some of their heat to the outside world. Even temperature is important: it's what prevents a steak from leaking its juices everywhere the moment it's been sliced open.
Because a sous-vide steak cooks from edge to edge with more or less perfect evenness, there is no temperature gradient inside. A medium-rare steak should be 130°F from the very center to the outer edge with only the outer surfaces hotter after searing. Sous-vide steaks can be served immediately after searing. The very minimal resting they need will happen on the way from the kitchen to the table.