Most beam weapons have a damage drop off. They do max damage at close range and zero damage at max range. The beauty of the very long ranges of lasers is that they retain more of their damage at higher ranges. So even though the range of engagement is limited by the BFC, it is still worth research laser range because it increases damage output.
Plus, while this doesn't help the huge long-range laser, the same tech does help small lasers you might want to use for ranged anti-missile or anti-fighter duty get more useful reach, if you're willing to pay for a big enough BFC.
