It heats the choke, that’s all. Of course the carb is calibrated to account for the air being pulled in through the choke stove. BTW, if the choke stove in the exhaust cover is burned through, exhaust fumes will be pulled in through the choke to the intake manifold and screw up the running. Also, some people can’t stand seeing the open fitting which is the choke stove air intake and plug it up. That also changes the air/fuel ratio entering the intake manifold.

EDIT: What I’m calling the choke stove is more properly called a heat exchanger—I think.