I would suggest that doing a normal departure offshore at night with a TDP of 20ft when you might be 90ft above the sea surface is a different proposition to an onshore helipad departure with a TDP of 35ft when you are at ground level and surrounded by obstructions and in fog, and becoming IMC during the vertical climb.
there is clearly a greater margin to correct mistakes offshore.
I have done both profiles many times, but do not fly in weather that makes me IMC doing the onshore profile until the appropriate time.