it is less typing, and less data. save the planet.

'd' works too, or did for Leibniz..

'Δ' must be a sign of Greenpeace membership, then.

Only if you've memorized how to type it. If you have to Google it beforehand, it serves as cheap signaling at best and an environmental transgression at worst.

Speaking of reddit, there is a subreddit called /r/changemyview where you can award deltas (Δ) to people that have changed your view or provided a particularly compelling insight.