Its a forward for when player types in console "impulse <number>"
Like for example flashlight.I know theres some impulse for nightvision idk how does this optimise the game engine by having impulses but it has its purpouse and with that forward u can hook them.
You can hook ur own impulse numbers there so say if a player enters impulse 1337 he gets 100% hp back u can do that like this:
PHP Code:
public client_impulse ( id, impulse )
{
switch(impulse)
{
case 1337: set_user_health(id, 100.0);
case default: return PLUGIN_HANDLED;
}
}