He's got the correct idea.
If you have too much ignition timing, meaning too may crankshaft degrees before the piston reaches Top Dead Center (TDC), then you will experience detonation.
If all things were equal, you could fire the ignition at TDC.
But they are not on planet Earth.
If you wait until the piston reaches TDC to fire the ignition, then it's already on it's way back down during the Power stroke before the burning Charge makes any pressure, and you have wasted much of your Power stroke.
The idea is to light the fire a little sooner, (before TDC, on the compression stroke) so the fire has a chance to consume all of the fuel in the chamber. By doing that, the Heat produced by the fuel expands the gasses in the chamber rapidly.
If you have the time you start the fire correct, the pressure will peak just after the piston passes TDC and starts down so the pressure can have maximum time to push on the piston and make horsepower.
If you fire the ignition too soon, the pressure will peak too soon, and try to push the piston back down the way it came.
That's VERY BAD for parts! (Not to mention your wallet!)
I'm sure you have heard detonation before.
Sometimes called 'Spark Knock'... Like when you are going up a hill in too high of a gear at too low of an RPM or hauling too much of a load...
You give it a little gas and it goes away...
(That's because you opened the throttle blades a little more, the vacuum went down, and some of the vacuum advance was lost, less advance means the ignition was firing closer to TDC and not way too soon.)
It's a rattle, knock, sputter, or just usual noise when you are cruising along with the throttle steady in a higher gear, and you hear something that goes away when you shift down, slow down, or give the engine more throttle.
If you find your engine is making noise like 'Spark Knock', back the timing down a couple or three degrees at a time until it goes away.
I'd also take two or three (at least) degrees away after that to make sure you don't have detonation problem you can't hear, or buy one of those knock sensors you can just mount on the dash....
We are coming up on a generation that has never heard 'Detonation'...
Every fuel injected vehicle I know of has a 'Knock Sensor' and retards the timing to get rid of it before human ears can even detect it!
MSD makes a gadget (timing control) that you can adjust your total timing from the drivers seat. It will work with the stock '78 to '90 Jeep distributor/module.
MSD also makes a remote knock sensor. That's the gadget I spoke of earlier that allows you to detect detonation you can't even hear yet. MSD P/N 8964
Combine the two on your dash, and you can maximize your ignition timing without detonation no matter the fuel quality, load, engine speed, or atmospheric conditions...
Easy to install, and damn near bullet proof! (Under $250 for both)
So many cats, so few recipes...