If you have older diesel cars, a minute or two idling would make it run better from cold starts (example - sa umaga). More than two minutes means you have other problems.

Same with gas. With some older cars the driver believes it will run better when warmed up. Usually this is true because your oil and oil pump are so low in the sump that it takes a little warming up to get it up to the piston area. A cheaper way is to make sure your oil is closer to HOT spot from a cold engine (unless specified in the manual na dapat turn on mo engine before reading the dipstick) thus it reaches the pistons faster.