Spoke plucking

Plucking spokes is done for the following reasons:

It's a fast method to check if the spokes have the same or very similar tension. It is not done to quantify the tension.
When performing truing operations it tells you which spoke(s) to adjust (see book for details).

Using a wooden truing stand naturally amplifies the sound when you pluck a spoke (think acoustic guitars and piano soundboards) and that's just one of the benefits of a wooden truing stand. I personally use a wooden stand and there are detailed plans in the book if you want to make one yourself.

Here's a video of a wooden truing stand in use by a reader of the wheelbuilding book.

Spoke plucking

Easton Wheels

This is the wheelbuilding facility at Easton Wheels. The building and spoke plucking starts at 5:15

Points to note in the video:

Balanced tension results in a wheel that stays straight and true.
They use an electronic pick-up to amplify the sounds.
Wheelbuilding is a compromise between balanced tone, radial trueness and lateral trueness.