Coming from Photoshop, I'm used to being able to create guides as I need them by clicking and dragging from the rulers onto the canvas, regardless of what tool I have selected at the time:
Creating guides while using the pen tool is quite useful.
Trying to learn Affinity Designer now, I've noticed that this is not always possible; Creating guides by dragging from the rulers is only possible when using the move tool:
This means that it is not possible to place guides to help you align nodes while in the middle of drawing a shape with the pen tool. You have to switch back to the move tool instead.
Since, as far as I can tell, there would be no contention with other UI interactions (dragging from the rulers to the canvas when not using the move tool never seems to do anything), I feel that the same behavior observed in Photoshop should be implemented in Affinity Designer. It would really help streamline things for designers that use guides as part of their workflow.