[WJW]

Hohmann transfers (the most efficient path) take a fixed amount of delta-V, so how much fuel you have does not really matter. You could probably find a quicker path if you are willing to sacrifice some efficiency, but even then it is going to take several years to get there with current technology. Since probes don't really care about travel time, might as well take the most efficient path so that you have fuel left over for interesting maneuvers near the destination.

[Valgrim]

Or more interesting probes, such as deep-drilling equipment