In some of the older cars there was an inline valve in the heater hose. That would shut off the coolant flow to the heater so you didn't get the hot air inside in the summer.
The trouble was that if it was shut, and the thermostat was closed, then the water pump didn't have anyplace to discharge to. So, they created a bypass hose that allowed some water to get to the radiator while both thermostat and heater were closed.
On the Jeep there is no valve in the heater hose. The water flows through the heater all the time. Therefore, when the thermostat is closed the water pump isn't blocked. It can flow coolant through the heater core.
Due to that, you don't need a bypass for the thermostat and it can be totally blocked and still have coolant flow through the pump. ALso means you can't just block off the heater hose, you have to at least put in a bypass hose that goes from the heater outlet to the inlet. There does need to be a weep hole so that water can flow a tiny bit in order to get the hot water around the sensor and make it open.
Of course, if the thermostat fails closed you won't have any cooling, except the heater core.