The check valve is there to only let water flow in one direction. On my system if it was not there when someone turned on a hot water outlet in the house cold water would flow through the at rest pump into the dedicated recirc. line and eventually to the hot water tap. Of course at the same time hot water would flow from the water heater. But the hot and cold would mix and you would not get just hot water from the water heater, decreasing the efficiency of the system. This is my limited understanding, I ain't no plumber.
On my system I have hose bib also. This helps drain the system if major repairs become necessary and also to prime the dedicated recirc. lines after repairs. MY PUMP DOES NOT TOLERATE BEING RUN DRY.