Vacuum advance

Your engine has FOUR or FIVE important timing milestones. In order of importance, IMO, they are;
1) Power-Timing
2) Part Throttle Timing
3) Idle-Timing
4) Stall Timing
5) Cruise Timing
All except numbers 4 and 5, ARE DONE/MEASURED WITH THE VACUUM ADVANCE CANISTER DEFEATED

Peak pressure needs to occur at a very specific crank-position, in order to transfer the maximum amount of pressure to the flywheel. Generally, this number is in the range of 25 to 28 degrees AFTER TDC.
If the pressure occurs too early, the engine could detonate, and the power will be down as the engine fights itself.
If the pressure occurs too late, the piston is already racing to the bottom of the stroke, and the potential for performance is lost, and almost worse is that operating this way, a good deal of heat is pumped into the cooling system thru the cylinder walls............ which may lead to overheating, but if not, it will most certainly send a ton of heat into the underhood.
The goal of all these methods of timing control, for us streeters, is to get the peak pressure to occur in the magic 25 to 28 degree window, as often as, and for as long as, is possible..
Except from idle to stall-rpm, because usually, this results in operational difficulties.
Specifically at idle. At idle, it is desirable to reduce the power by delaying the pressure peak, to smooth initial transmission engagement, and to smooth drive-away on the fluid-coupling at Part Throttle. Yes the engine will be snappier with more pressure, (created by earlier timing), but there comes a point where your gas-pedal starts to feel like an on/off switch, and if it happens at an rpm/load setting that you are often in, that becomes very annoying. This is especially annoying with a tight lo-stall TC, and majorly annoying with a manual transmission..

If you defeat the V-can permanently, your engine will be running 100% of the time, on the PowerTiming curve, which is usually adjusted to be as close to the maximum amount of timing your engine can take, at WOT.
If you run your street engine this way, most of the time, the engine will not have nearly enough timing. And so most of the time, the engine will be lazy, and will be sending unburned, or still burning fuel, into the headers. In the headers it will destroy your overlap cycle, which at idle is not a bad thing. But as the Rs increase, you want that Overlap cycle working. The harder you step on the gas, the closer the timing will be to ideal and so, this header-pressure screw-up goes away.
at Part Throttle, with the peak cylinder pressure now seriously reduced by the late PT timing, the engine is very lazy and responds slugishly. With a 3500TC you might never notice it, but at the lower rpms involved on the street, oh-yeah, you will be very disappointed.
At cruising speed, most street engines will want timing of 48 to 56, possibly as much as even 60*. So, by only having 30 to 36, guess what happens to your fuel consumption...... your engine,
"will be sending unburned, or still burning fuel,into the headers"

Consider this;
at about 2800 rpm, your Power-Timing might be 28*. But the Vcan could be bringing in as much a 24 additional degrees, so, then she might be cruising on 52*. But at Part-Throttle, your foot-feeder is simultaneously controlling;
BOTH the fuel/air charge,
AND the timing;
between 28 to 52 degrees,
depending on how far the throttle is open. How cool is that!

That's about as short as I can make it, and it still be meaningful...... lol