For some beam weapons, there is damage drop-off as range increases, and having a higher range modifier reduces this drop-off so you can output more damage at longer/maximum range. I believe this is the case for lasers, railguns, and plasma carronades, although it only really matters for lasers since the other weapon types don't exceed BFC range very easily.
This is a problem with the tech progression for mesons and HPMs, as has been discussed elsewhere especially by xenoscepter.
...Yes, I'm aware of what the range modifier
does. The point is that, as the range modifier techs seem to linearly increase the cost (at least for lasers), large lasers have quite significant damage, and beam fire control range is limiting, you can save considerable mineral and BP investment at a comparatively small cost in performance.
For instance, right now my max BFC range is 384kkm. I just designed a 45 cm (advanced spinal) laser, 53 muzzle energy. With the Near UV (30kkm range increment) tech I chose, it should lose 12 damage and deliver 41 damage at max BFC range. If I'd built it 2/3s more expensive with Far UV (50 kkm) tech it would instead lose 7 damage and deliver 46, which hardly seems a good return on investment (though it'd be slightly more useful for STO since those have an extra BFC range boost). If downgrading range tech further I could have had it lose 19 damage and deliver 34 or lose 38 damage and deliver 15 (at a very low price), but I opted against those.
You could also say the same range attenuation applies to Gauss, they just don't have caliber scale-up so damage per shot is always 1 and their max range is 1 range increment.