OK two huge reasons you should reconsider. Let's consider a situation to use as an example: Say you're outside where its reading 3600. Then you move inside where its reading 100.
1) Even though your in an area where your phone is reading 100, since it's taking an average based on the past as well, it's going to be basing its value partly off of where you just were (outside) rather than basing the brightness entirely on where you are now. The deviation between our 4 descrete detected values is so great, that having the light sensor filter on will actually decrease the accurate correlation between environment and screen brightness.
2) Having the filter on can make you hit a point within a range as you said, but you need to realize it doesn't have the ability to last. Even if you set your window length to 60 seconds, your filtered brightness is going to quickly dive and then slowly plateau, finally hitting a flat 100 after 60 seconds has passed and that last 3600 reading is out of the picture.
And BMc08GT, I saw your settings... you have your Reset Threshold at 400lux. That right there means that your filter is only "good" for 2 values: 10 and 100 and only when they change between each other. If you go from 10 to any number beside 100, or from 100 to any number beside 10, your filter is going to instantly reset anyway. I'm only trying to help you when I tell you this, because its painful to see those settings in a thread dedicated to saving battery, having the filter on is a huge waste of cpu especially since you are only using it in 2 out of a possible 6 scenarios, and even then it only lasts for your window length of 30s, and even then it is causing you to have a reading that isn't entirely based on where you are. And anything that wastes cpu is wasting battery.