How to use Node Extrude:

1. Use the Shader Editor
2. Hover your mouse over a node
3. Press the Hotkey ("E" by default) and hold / Double-click-and-Drag
4. While holding down the shortcut, drag your mouse to any socket on the node
5. When highlighted, release the shortcut, a context menu appears
6. Select a node from the list of smart suggestions (listed nodes depend on node and socket type. Only most useful nodes are listed)
7. Hold shift to insert the new node between connected sockets (behavior can be changed in preferences)
8. New node is being created!

The context menu is different for each socket type (and might vary for specific nodes). Node suggestions are categorized into "general" and "direction-specific" (depends on if a socket is an output or input). Custom icons provide even more clarity. Context menus are kept small enabling a faster workflow BUT this will mean that some nodes will still need to be added the "traditional" way. Context menus will have you covered around 95% of the time.