In my V12 Jaguar days, these were MANDATORY (2 per car) because 7/10 times the PO put Bars Leaks in at some point and all kinds of other crap, so there was always junk floating around the cooling system. I have one on ALL of my vehicles.

Plus, you never know if there's core sand left in there or casting flash that has broken off...I think it's good insurance, but they're more $$$ now than they used to be, last one I bought was $50.