I would like to have a hotkey to lock the "ghost", that you see after selecting something from the build menu, in place so that it doesn't move when you move around. This would be very practical when aligning big machines, as at the moment you sometimes can't see the part of the machine that you want to align. I know that you can already hold ctrl to to align the middles of machines but this doesn't help if, for example, you want to align the input of an assembler with the output of a constructor.
This is a little hard to explain, I hope it's understandable what I mean
EDIT: I just noticed that there is actually a green line to show when an input aligns with an output, even if it's not at the center of the machine. Though the feature I suggested could be convenient anyways.