The hot water inlet is there to prevent icing in the throttlebody caused by the drop in air pressure that occurs there.
Icing can cause the butterfly to stick or the engine to lose power and eventually stop.
High humidity combined with low temperatures, high altitude and small throttle openings (ie high vacuum) will contribute to form ice in the throttlebody.
Thing is you never know when it is going to happen. Throttle ice can happen any time the conditions are right, even in summer.
This is a well known problem in light aircraft and anybody who has done any flying gets very quickly acquainted with the carby heat lever on the dashboard which diverts hot exhaust air into the intake manifold to pevent ice build up.
Too much ice will give reduced power or may even stop the engine.
Engine stoppage on a light aircraft = bad news.
In modern cars, rather than having a manually operated hot air inlet system, it is usually automated by a thermostatic flap that can alternate between cold and hot inlet air depending on the ambient temperature or there is a continuous hot water flow system to keep the throttlebody warm to prevent icing.
Icing is not so important on our cars as you are not going to crash, but I would be reluctant to disconnect it anyway. Throttle icing is not something you need.