It basically opens up the throttle body to let more air flow through. The The only real world experience I have is on a 1.9 L saturn. I have data because we swapped throttle bodies at the track on some back to back runs. It netted a 2/10 second reduction in the 1/4 mile time.
Let me add that this was a bored out throttle body. The butterfly was taken out and the throttle body was reamed out about 1/16". That's about the limit while keeping the integrity of the metal without making it too thin. Of course a bigger butterfly was made. This wasn't something I did, just an example of an aftermarket throttle body using a stock one as the core.
The amount of obstruction removed is similar in both examples.
The problem is "feeling" 1 or 2/10 of a reduction in 1/4 mile times. Some can, some can't. Most "can" when it makes a noise. That adds a sensation to the driving experience. Examples are exhaust and intake- they make noise.
I've done it on mine and we did Kevins truck. Kevins 3.0 should run in the high 15's next time at the track. At high 15's in a 3.0 the mod didn't hurt anything that's for sure.
2004 Ford Ranger Sonic Blue 4dr 4x4 4.0 Manual