As Cal844 said, there is a bodge just as bad as glue together CV boots, you can get a concertina hose about 2" long that goes between the water pump and the head. They are known to fail. Maybe last owner had one blow and just siliconed it shut and swapped the pump for a non bypass type. Or maybe ordered wrong pump and just siliconed it closed.
Dont think there is any benifit with it closed just causes the head to warm up slower as the water cant circulate around the head it has to do the whole loop .