Tiny "trick".

There may be occasions where you wish to create a symmetrical node to a closed shape. By "symmetrical" I mean ... another node is exactly positioned ... vertically or horizontally on your core shape ... as a "reflected twin".

(My definition of "symmetrical" node above differs than the standard definition used within Inkscape.)

This can be done by other steps, but getting that desired node "exactly positioned" may be troublesome. (Even using the Path Effect Mirror Symmettry may be a task, as as you move the reflected shape, it may destroy a node or two that you want to be "reflected".

The steps below may be helpful.

The starting shape must have some symmetry in it to begin with. And be a closed shape.

You simply (1) add your node to your shape, (2) duplicate the shape, (3) fllip it horizontally or vertically, and then (4) combine both shapes together.

The end result show have your nodes added, symmetrically.

See the graphics below.

Enjoy.