Purpose of the chain link icon in transform tools

[Ofnuts]

Anyone know the purpose of this chainlink on the right of the Direction choices?

   

[tmanni]

This allows moving handles without affecting the transformation, letting you manually readjust the initial shape before applying any transform.

[rich2005]

Came in with Gimp 2.10.10 From the release notes:

Forward and backward transform directions can be linked,
which allows moving the handles without affecting the transformation,
letting you manually readjust their position.

Still not exactly sure what that means in practice.