It used to be as simple as "ear muffs" for running fresh water into an outboard, spraying some fogging agent into the carburetor air intake, changing the lower unit gear lube, clean and lube the prop shaft, change the zincs and Presto, it's done, let's watch football !

Ok, with an older two cycle engine that may still suffice, but modern four cycle engines need a bit more love and attention.  

(plan on recording that game on the DVR).   

Is Flushing Necessary ?    

For fresh water boaters, probably not. For saltwater engine use, ABSOLUTELY ! Saltwater is a silent, corrosive killer that can corrode aluminum and accelerate rust on steel. It also leaves behind salt deposits that can build up inside the cooling passages of your engine and cause blockages over time. Flushing also will remove residue debris, silt, sand and some marine growth.