What is benefit from that option? I'm mining with i5 cpu and one 280x. It is good option for cpu miner or big rigs??
The fixed difficulty option allows one to select a difficulty which seems appropriate, without the pool trying to adjust in real time. In the long run, it should not matter, but some people prefer this to avoid the ramp up time when reconnecting on a variable difficulty port, where difficulty will start from a set value and then adjust to the miner's speed. It will also reduce variance since you avoid the case where a string of lucky share finds pushes your difficulty high and get a long time without a share. All a wash, I think, in the long run.
The option will have the most effect is when your miner settle on a difficulty that's far from the starting one (which is 1000 on my pool), so GPUs would be the best suited for it. But, again, in the long run, I don't think it makes much of a difference.
