Torque converter question

dumb question but what happens in a transbrake application when the stall speed is c lose to the launch speed? Does it work the same as dumping a clutch? What is the reason for running a high stall in a t-brake car? say you launch at 5k on a 5k verter. why not just use a lower stall and maybe larger case say 10" or 11" vs. a 7" or 8"?