Photographers: how do you decide which evening is worth going out for a sunset?

Asterfold: Sunset Planner launches here on 8 November. I'm one of the makers.

It's a sunset planner for the places you actually watch from. A sky dome draws the Sun's real path for any place and date, coloured by golden hour, blue hour and twilight. You save the exact spot you shoot from, turn toward your shot on a first-person horizon, and pick your lens (14 mm to 200 mm, or your phone's camera) so the frame matches. It's calculated on the iPhone, so it works offline at a remote viewpoint.

A question for landscape and city photographers: when you decide whether tonight is worth the trip, what do you actually check? Cloud height, the Sun's bearing against a landmark, the tide, something else? And how often does the sky prove you wrong?