Trahan's method is in line with other vertical /steep backswing methods. Leadbetter advocates a vertical / steep backswing for example. A vertical / steep backswing works for people who have difficulty shallowing out in the downswing, which is a lot of golfers.
In order to lay the shaft down in the downswing you need to be able to externally rotate your shoulder, which for many is nearly impossible to do. Many golfers shallow early and steepen late, standing the shaft up at impact. For these golfers standing the club up in the backswing (vertically) allows for a shallow downswing.
A steep backswing allows for a natural shallowing in the downswing for these golfers who can't externally rotate their shoulder in the downswing. The important thing to remember is you don't have to adopt the whole concept in any method. You can take bits and pieces and use what works for your swing.
And since all we have is feel, you just need to have the intent and that will be sufficient for many golfers. Remember every golfer has faults in their swings. It's how you negate or manage these faults that's important.