Ask OP why he needs to dump fuel that is used to jump in the first place (I understand why, it already got explained in here, don't care to repeat that).
Or any other explorer why they fit shields/hangars/heat sinks or other utility that adds weight. Probably to use it.
If you don't care to carry plasma slugs to use this feature, then it doesn't seem that highly sought after. That's all I'm saying.
I think you miss my point. Everything you mentioned that adds weight, serves a function.
Shields - minimise the damage from a hard landing.
Vehicle Bay - allows planetary exploration.
Heat Sinks - prevent heat damage when flying too close to a Star.
Fuel - is required to power the ship.
Yes they all add weight and reduce the jump range, but they all have a particular job. Many explorers even choose to go without one or more of these modules simply because they do exactly that, add weight.
Plasma/Rail Slugs - ??? I'm at a loss. Literally the ONLY purpose for these things (as far as exploration is concerned), is to dump them to decrease the weight of our ships and, by extension, increase the jump range. But if that's the case, why bring them in the first place when we could simply not have them at all and have the extended jump range from the instant we leave the station?
Dumping fuel would allow explorers (and indeed others) to extend their range for whatever purpose. Be it to reach a scoopable star, or to take a shortcut.
To give an example from personal experience: I was in my Python in the Daramo System when I recieved a mission asking me to travel to the Coelatuvean System, 12.46Ly away. The maximum jump range on my Python was 13.4Ly (approx), but my current jump range was 12.27Ly. This was simply because my fuel tank, when full, added an extra 32T to the total mass of my ship. Being able to dump 2 or 3 Tons would lighten my ship and allow the extra 0.2Ly required to make this trip in 1 jump not 7.
Yes, I could've fit a smaller fuel tank but my point is to demonstrate how this could make a huge difference to the explorers over 25K Ly away from any known stations.