I would look at it like this. What does the girdle do? Helps prevent cap walk. What does cap walk do? Under extreme conditions such as high rpm's or detonation or both, the caps will actually lift off the block registers and bounce leaving small marks on both the caps and block registers. When those caps are bouncing off the blocks cap registers ,the webbing around the caps can fatigue and crack.. Them BOOM in some cases..

With that said, if you have the opportunity to HELP prevent the main caps from walking that could ultimately lead to the webbing around the blocks main cap registers cracking and BOOM, I really don't see a reason why you would not want to HELP the main caps from walking/bouncing with the use of a girdle. Aluminum caps is a big big help as well......