It's completely unnecessary to warm an engine at idle before driving off. It just wastes fuel and contributes to combustion chamber build-up, which is not good either. Every 3 minutes of idle time is equivalent to 1Km of driving in terms of fuel consumption. The manufacturer actually states that extended warm ups can damage the catalytic converter, which then contributes to poor engine performance and environmentally damaging emissions.

Drive it as prescribed in the owners manual, best policy by far.

GeeeAus