I almost never go out of my way for fuel, because as you say, it's rarely worth it once you factor in your time (never mind the fuel spent).
But it's still useful to know about price variation so that you can plan ahead. I regularly drive past several different petrol stations, and if I know that one of them is usually cheaper or usually more expensive then I choose to use or avoid it, or to decide that I'll fill up tomorrow when I'm going that way rather than today at a more expensive one.
And that'd be more useful built into satnav, so that if I know I have to fill up somewhere along my route then I can pick the cheapest place, since there's no real time cost to any of the options compared to each other.
But it's still useful to know about price variation so that you can plan ahead. I regularly drive past several different petrol stations, and if I know that one of them is usually cheaper or usually more expensive then I choose to use or avoid it, or to decide that I'll fill up tomorrow when I'm going that way rather than today at a more expensive one.
And that'd be more useful built into satnav, so that if I know I have to fill up somewhere along my route then I can pick the cheapest place, since there's no real time cost to any of the options compared to each other.