The difference is being able to make the most amount of HP available & having your engine work in a safe detonation free environment.
If you retract timing in all your cylinders so it does not detonate, you will lose the most amount power output doing it that way.
There are two modes the J&S can work in, retard ignition in all cylinders even if only one cylinder is knocking, (safer that way) or have it selected so it will only pull timing in the cylinder/s that is detonating. Not as safe, but will make more power.
Every engine is different, there is no one set valve for total timing for a turbocharged engine.
If you choose to use a MSD BTM ignition unit, that is great. But as I have told you all along, you cannot always hear detonation, as your last two engines proved.
If you still plan on running an open pipe exhaust, no muffler, you are never going to hear the detonation that has been tearing apart your engines.
Having an extra 2-4 degrees of timing could be another 20-30+ HP.
I hope you do get a knock light to help w/your tuning. They are available.
You can use that (a MSD BTM ) & pull back a lot of timing so the engine does not detonate, but personally I do not like the idea of leaving available HP on the table that I am not using, it frustrates me, maybe you are OK with that concept?
Think of it as if you are only using 3/4 throttle, but you have another 1/4 throttle left, but you are not using it.
The problem with having just a knock light, is that you cannot always be looking @ gauges to see what it going on, it is unsafe to be driving that way anyways. With electronics they can monitor what is going on w/your engine & automatically change the settings so your engine can operate in a safer environment, which will be for the better,, & safer it will be for you your engine & your passengers.
Just like what is available also, if your engine is detonating, there are devises that will reduce your boost levels also in case your engine is hearing detonation. It will make your turbos wastegate open & reduce boost pressure.
The MSD BTM box has only a certain amount of timing it can pull.
The J&S can pull more timing than a MSD BTM.
When I had the Paxton supercharger blowing through the 3 DCOE carbs on my 250 inline 6, I did not have a knock devise, (MSD B.T.M) a J&S safe guard or anything like that.
I just played it safe & had run low total timing, but I was also probably leaving another 30-50 HP available on the table.
I have used forged pistons & glad I at least had those in the engine because I am sure if I ran cast pistons I would have grenade my engine a few times from the bad detonation I had heard.
