In most cases, a check engine light does not mean that you need a tune up. This is a common misconception. At times, there can be misfires which are caused by bad spark plugs. When that happens, the vehicle will run poorly as well as causing a check engine light. However, 90% of check engine lights are for other reasons. So to just assume a tune up is wrong about 90% of the time.
Tune ups should be done for maintenance before a problem surfaces. The definition of tune up can be (and usually is) greatly debated.
As time went by, manufacturers replaced the distributor with coil packs. This created the distributorless ignition system. The advantage was a better spark to burn fuel more efficiently. The draw back was more expensive spark plugs and wires to carry the spark. So even though a distributor cap and rotor are no longer needed, the price of the tune up went up to $250-$300.
Of course, technology is always changing, and vehicle manufacturers are constantly changing too. So, to take things a step further, the COP ignition was developed. COP stands for coil-on-plug. So now there is no coil pack or plug wire. Instead, each plug has it's own coil that is controlled by the vehicle computer system. This, paired with the modern fuel injection system, creates a much more efficient combustion system. So the tune up requires only spark plugs, fuel filter and air filter. The drawback is that the new spark plugs are platinum and are at least $10.00 a piece. A tune up on these vehicles can still be about $350.00 because the fuel system service is now a part of it. To keep the fuel injectors working properly with the new ignition systems, performing a fuel system cleaning is often recommended.
At the very minimum, a customer can replace spark plugs every 60,000 miles for about $100.00 at most shops. The cost can be spread out by doing the fuel filter and fuel system cleaning at the following visits.
The best rule of thumb is, don't do a tune up because you think you need it, do it before there is a problem and you'll experience fewer problems.