[constructor]

IMO the shims are used so you can get 40-80lbs and have your barrel nut gaps(gas tube slots) align without going over the 80lb max.
We started using bedding back in the early 90s when the tolerance on the receivers wasn't near as good as it is now. If you have an interference fit like with Vltor, Mega and the BCM (Thermal) you may not need to use bedding. Anything that improves the rigidity of the barrel to receiver connection should help accuracy.

 

[constructor]

If you can't get them tight they are useless. If the plan is to wrap the extension until you can't insert into the receiver and then heat the receiver that would be the same as the thermal fit BCMs.

 

[constructor]

If the aluminum distorts to fill the gaps it would squeeze all of the bedding out but it doesn't.

Most people wouldn't notice the difference of a bedded extension and a non bedded because they just go to the range to shoot short distances or make noise with inferior barrels but those interested in better accuracy especially at long range should do it.
Derrick Martin of Accuracy Speaks fame was the first I remember talking about it in the 90s when he was winning all of the highpower competitions. He wrote the book "The complete guide to AR15 Accuracy"(focused on highpower comps) I trusted his advice back then and tried it, still use the same procedures as far as squaring the receiver and bedding.

 

[constructor]

This article suggests that if you think you need to bed your barrel, you probably have a bad part. Also, once you put the torque on the upper, the aluminum distorts to fill the space.

I think their reasoning makes sense.

Smyth Busters: Should You Bed an AR-15 Barrel?

To bed or not to bed? Steve and Caleb weigh in on whether your AR-15's barrel needs to be "bedded" into the receiver.

www.brownells.com

The parts Brownells sells need to be bedded so maybe they need to make better parts. IME Vltor and Mega were tight enough that they didn't need bedding, 10 years later BCM is making their receivers smaller dia to the point they must be heated to insert the barrel extension.