Bruno Gousseault one of the fathers of sous vide cooking recommend browing before for a couple of reasons; Browning on high heat will help eliminate surface bacteria, and in the other hand, because sous vide keeps and amplifies flavors your food will be infuse with the flavors created by the Maillard reaction, which is pretty cool. Just make sure that when browning the core temperature doesn't go above 30 degrees Celcuis. After cooking you sear it again for service. Cheers n.