It's for instant hit weapons (rail, shotgun, machinegun and lightning gun, you can turn off/on any one of these because the variable is a bitmask), and its effects are best seen with higher pings. What it does is to remove the delay that between the time you shot these weapons and the time you see the shot on the client, as if you would have 0 ping. This is a client command, so it wont affect unlagged or anything alike. I like the concept of the feature, but currently it has too many bugs, so i would suggest to turn it off.

wrote:

These are the bitmask values, right?
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1 - LightningGun shaft
2 - PlasmaGun bolt
4 - Rocket Launcher explosions
8 - Grenade Launcher explosions
16 - Bullets (machinegun и shotgun)
32 - Railgun
64 - BFG
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I remember i had xp_delagWeapons 15. So it means i had only GL,RL,PG,LG delag ?

Nop, they are only 4:

1 Machinegun

2 Shotgun

4 Lightning

8 Railgun