What effect would shorting a Vin+ pin to GND have? Assuming no DC power has been fed and the board is not connected to power. Would damage the board or has no effect?
If the board is not powered, there should be no effect. There will be a short but there will be no (significant) current flowing.
It should cause no problem if the power is not applied. However, if you do this with the power applied, then the low resistance path may cause a large current to flow from Vcc to GND, damaging both pins if no protection is provided.
Nothing happens cause you don't have any power applied to the board. If you would have a powered up board and short 5V and GND for a short period of time probably nothing would happen. The consumer Developmentboards are wery resistant and have security features to prevent serious damage.