In Mr Grumpy's pinned article on optional rules, the comment for both Optional Fire and Assault Results is a laconic "Do not use unless set by default, for more info see the OR help section."
By OR help section, I assume that the main program guide is meant, and that simply says the effect of both is to average two results, thereby limiting variability. So why not use these two options? What am I missing?
As long as you have read the effect of these rules then go ahead and use them if you feel they will enhance your game, in my article I can't give any guidance on how they might affect play balance in a particular scenario as I have never used them and I don't ever recall a conversation about them on the forum.
The manual suggests their effects are quite benign, but none of the titles released up until the Japan titles were tested with these rules on.
My assumption has always been that these optional rules were included simply to allow for those who wanted to remove some of the element of luck from the game and so make it a fairer contest. Consequently, not using them presumably reflects the level of variability that is believed to more realistically simulate actual combat.
Apart from their use in the Japan games I have never encountered anyone wanting to play with these rules selected. Personally I would not want to use them and I would not mourn their loss if they were removed as options. Of course, others may think differently.