Just looked into FIP. Looks like this is considering HRs, BBs, HBPs and Ks as the only things that are meaningful to a pitcher's effectiveness. These numbers are plugged into a formula:
FIP = ((13*HR)+(3*(BB+HBP))-(2*K))/IP + constant
in which the constant is the same formula (without the constant), using numbers for the whole league:
FIP Constant = lgERA - (((13*lgHR)+(3*(lgBB+lgHBP))-(2*lgK))/lgIP)
So, what you are really doing is looking at things that are ONLY in the pitchers control and then comparing what you do against the league average. You're doing good if your FIP is below the constant (league average) and not good if your FIP is above the constant (league average).
Here's what they say about the weights given to the different categories - "The individual weights for home runs, walks/HBP, and strikeouts are based on the relative values of those actions with respect to run prevention." and I'm not sure where they came up with that.
This is OK, but it seems to me that there are other things that help determine a pitchers effectiveness other than HRs, HBPs, BBs and Ks. There is always talk about how ground ball outs are much better than fly ball outs for example. There will always be balls put into play and to not consider the mix or even consider that balls are put into play for a pitcher in measuring his effectiveness, leaves a lot out of the equation.
This may be one tool to use in measuring the effectiveness of a pitcher, but I don't think it can be the only one.
You could potentially have a pitcher with a VERY low FIP if he doesn't give up many HRs, has low BBs and a lot of Ks. But what if he gives up a TON of gappers and gives up a lot of runs. Not sure I'd want that guy. We had a guy that would have outings like that on one of my son's teams. He would strike out the side, but would give up 3 singles and two doubles in between the strike outs. FIP would not take any of this into consideration.