In what I was always taught is the maintaining of the connection of the two parts is the most important factor, the bolt is not the connection point, it is there to maintain it, the problem happens when we put steel bolts in to hold together aluminum buss or lugs, as aluminum will expand faster then the steel, and when it cools it will be loose because of cold flow of the aluminum, this is where bevel washers come into play, bevel washers act as a spring to allow the aluminum to expand and contract without the cold flow, this keeps the connection between the two parts for loosening up.
With that said, I found a few manufactures that stopped or never did use any kind of expandable connection, many of square D panels will have the bevel washers while T&B never had them, T&B were always failing on the buss connections, I still have a small selection of bevel washers in my truck, from 1/4"-3/8" that I use when I run across aluminum busses or lugs.