That's true with many things, such as throws, props, etc., but it's quicker to get where it feels right if you are starting from a close baseline. The 30% - 33% isn't a hard-and-fast "rule;" it does provide a very good starting point though and is better/quicker than arbitrarily moving the CG hoping to get it close. It also helps to remove a possible variable (CG) when trying to figure out why something is happening such as having to carry a lot of trim. Unless the plane wasn't designed within "conventional" parameters, if the CG is in this range and you are still having to carry a lot of trim, there's an issue somewhere else.

Sure. It sounds like it may help rule out a CG issue.

Using the trimming methods outlined by Peter Goldsmith takes a while, but when finished a plane flies so much better.

Dan