If there is nothing wrong with your car, then the engine should start up right when you turn your key. In the background, there is a whole bunch of other things that happen at the same time to help your car get started. The Electronic Control Module makes the ignition coils deliver power to the spark plugs. There is a gap in the spark plug that makes a spark in your engine cylinder. It ignites the fuel and makes the piston go up and down. The engine starts spinning after this which makes the wheels turn, and you drive away.
Ignition coils are basically copper wires that are wrapped around an iron piece. There is usually an ignition coil for each spark plug. So, like there will be six coils for six cylinders. Now, speaking of ignition coils, when they start failing your engine begins making startling noises, and the check engine light starts flashing. A tired and old spark plug can lead to the failure of the ignition coil.
Thus, it is important to carry our preventive maintenance of the spark plugs, and change them on schedule. Besides, ignition coils cost way more than the spark plugs. Having a bad ignition coil can drastically affect the Electronic Control Module. Repairing the Electronic Control Module can be really expensive. Thus, ignition coils are so important for your car. But, to make sure that the ignition coils are in proper working condition, you need good spark plugs.
Thus, though both premium ignition coils and premium spark plugs are important for your car, the latter is slightly more significant. Besides, buying premium spark plugs will cost you much less and it will also help in keeping the ignition coils healthy for a long time.