It depends its used for colder climates so people can walk into a nice cozy car instead of a nasty freezing col seat etc. it is not necessary for warmer climates bcuz then you'll get overheated. Not sure if that's what u meant but I tried:)
In frigid climates it is necessary. The oil needs time to circulate through the engine before you take off. Even in warmer climates you should not just start it up and take off...give it a few seconds...it'll help prolong your engine life.