When reorganising a node network, you often want to move all the nodes upstream from a particular point in the graph. You can Shift+Alt click to select all such nodes and drag them to a new location. Here’s an example moving some nodes to make way for the insertion of another node. Also note how the node is inserted automatically when dragged over the noodle.

Upstream Selection Animation

Alternatively, you may want to do the same but with all the downstream nodes. For this you can use a Shift+Ctrl click.

Downstream Selection Animation