I only sear meat on one side for the best balance between flavor and speed. Browning adds a lot of flavor to braises when the cooking liquid melts the browned bits stuck to the bottom of the pot. You can skip the browning step if you're in a big hurry, and the short ribs will still be good, but not quite as great as they could be. Or, if you have the patience, you can brown the meat on multiple sides to build even more flavor. "Brown on one side" is my compromise between flavor and speed.