I heard the suggestion in there of the general principle that Capers liked - the ability for your defense to play against a number of different formations without substitution. OK, so that's pretty much 'duh' but in practice it has to be pretty challenging. But given the number of offenses like the Packers that liked to run the 'hurry up' no sub offense, being 'multiple' with a base defense is essential. Oh, and nickel is base.