CMDR Athanasius' Route Planner is good for that.
This only uses visited stars in EDSM and requires the system name. This wouldn't really work for what I'm talking about.
OK here is an example. You are out on the rim of the galaxy trying to see how far out you can go. So you look farther off into the distance using the galaxy map, the stars are thinning and are very far apart so will require jumponium to make the jump. So rather than flying there and checking, you can click on a star, and set it as point A, then choose the second star (star B) and see how far it is from A. See if you will need a 1 2 or 3 level injection. And then you check the next star after that, and so forth. So you can determine your course before you hit a dead end.
I already have a distance calculator I made for stars where we know the coordinates, but you can't see coordinates of star systems in the system map.