Bottom line is whether one blocks the crossover or leaves it open is entirely up to the individual.
Personal opinion is that FOR STREET ONLY DRIVEN VEHICLES, the only benefit is the paint won't burn off the crossover! Trailered race vehicles are a different story.
Cliff said it very well (over a couple of different posts) in that based on ones' tolerence of cold driveability issues and how rich one is willing to tune the carb, and when the vehicle is driven; one can get away with blocking the crossover.
The solution on my own GTO on which I blocked the crossover was a manual choke carburetor. Even in 75 degree weather, the engine likes some choke for up to 30 minutes driving around town. (Or, I can push the choke off, and restart the engine at each stop light!). Too much HP/CI on a street engine and tuning is responsible. I chose NOT to just throw too much fuel at the engine! On the highway, I get fuel economy most of you never even dream of
with no detonation on pump gasoline (93 octane).
And I would NEVER again block the crossover on my own street vehicle.
But the choice is left to each individual.
Jon.
__________________
"Good carburetion is fuelish hot air".
"The most expensive carburetor is the wrong one given to you by your neighbor".
If you truly believe that "one size fits all" try walking a mile in your spouse's shoes!
Owner of The Carburetor Shop, LLC (of Missouri).
Current caretaker of the remains of Stromberg Caburetor, and custodian of the existing Carter and Kingston carburetor drawings.