In anything other than near zero or below temps there is no reason to warm up a cold engine, you are doing two things which are actually harmful, one is idling while the engine is cold INCREASES WEAR on the mechanicals inside it, and secondly it can decrease the life time and longevity of emissions components too, of course you are also wasting gas if it matters to you.
Folks stop bothering unless absolutely necessary like scraping ice and snow off the car windows.
Get in the car, start it up and GO!