Considering that the turbine pace lags all the time powering the impeller (pump) speed, the speed ratio is below one. Which means You can find friction while in the transmission fluid which results in power losses. The torque converter clutch solves this by locking the turbine for the converter’s housing, https://jeffreyvkykw.laowaiblog.com/32979363/how-torque-converter-clutch-can-save-you-time-stress-and-money