A FFIM will make it tons easier to change spark plugs or to do anything on top of the engine, really. The rerouting and shortening of the IC piping provides so many benefits, most of which have already been listed here.
Also, you get the benefit of having a tb flange for whatever throttle body you want, allowing you access to a wider selection of throttle bodies.
In regards to performance benefits, it's hard to judge the effect of just the FFIM. Sure it may flow more or whatever, but when you go from stock to FFIM setup you should also go stock IC hardpipes (upgrade from stock) and a decent quality FMIC (upgrade from stock) which alone will improve your boost response, plus you'll have less pressure drop across the upgraded FMIC vs. the stock IC. It's hard to compare apples to apples with an FMIC setup unless you've already got a side to side FMIC and hardpipes--in which case you've got even more piping than stock!