Why would you ever adjust your sights ?
The MG can be set from 200m-1200m.
Tell me one map, aside from the Gu-something tank-only map that is even 200m wide?
The longest shots you do in the game is 150-175m, the latter range being almost exclusively on FallenFighters.
On Spartanovka I've done 175m+ range shots with Kar98 (as you get the achievement it's very noticable when you do your first 175m range shot). Did I bother adjusting the sights up to 200m instead of 100m which is default on rifles? No... can't be arsed. The gun shoots straight enough at 175m with 100m range set. Put the crosshair on the center mass of your target, which is barely more than a handful pixels at that range, squeeze off a shot and you are pretty much guaranteed to hit (barring any other unforseen factors such as lag, target moving suddenly, grenade/arty landing in your face or bouncing your sights etc).
The bottom line is... adjusting the range on rifles and MG is a waste of time. On sniper it might help (though I rarely ever play sniper since I don't like the camping style of it). On tanks you might adjust the sights, although I can fire accurately clean across FallenFighters without bothering to adjust the sights.
The only time I ever really had to adjust my sights was on that Gu-something tank only map where you are firing at extreme ranges.
Another thing that comes into play is of course Identification-Friend-or-Foe (IFF). At 175m+ range, can you *really* know that the black/grey clump of pixels is an enemy, or could it be a friendly? Are you gonna open fire and risk blowing away a Squad Leader who spent the last 10 bloody minutes crawling across FallenFighters park, bandaging, praying no arty hits him during a barrage, strangling 3 enemies and battling a polar bear to get into a position to give his squad of 7 people a spawnpoint close to the front?
I dunno how many times I have been shot and killed behind, or near the enemy line, as a Squad Leader. I get my arse up there so the squad can maintain pressure on the front by not having to footzerg from base, and some triggerhappy, fraghungry, halfbrained camper with a scope (or even without) takes shots at me and kills me.
If you can't tell enemy from friendly (and you can't at 175m+ range, unless scoped or tank sights) then DON'T SHOOT. Sure, you can make an educated guess that it might, possibly, if the circumstances are right and with a bit of luck be an enemy you are shooting at.
So what then is the point adjusting sights at all? You need the enemy to be closer to be certain you are not shooting your own team anyways.
Unless, of course, teamplay is unimportant and kills outweigh the risk of teamkills.