Is "sealing in the flavor" an actual thing?
Searing on a grill to "seal in juices" has largely been disproven.  Meat loses juice at roughly the same speed regardless of searing the meat first.  Searing does produce the Maillard reaction and caramelization which enhances flavor; however, searing first doesn't produce better results.  A test performed by Alton Brown in 2008 demonstrated that searing at the end of the cooking process loses less water than searing at the beginning.  For more information see this link.

For the Alton Brown results see this link (video).