My STI engine ran just fine, and my boost numbers are right on with a large turbo inlet tear. I heard a faint squeal (like letting the air out of a balloon) that was barely perceptible at first, but slowly got worse. I knew to actively start looking for an issue when my fuel trims started getting wonky. The tear was post-MAF, pre-turbo, so it was sucking in extra unmetered air.
//
Again, I don't know how easily datalogs can be ported from phone apps, but if it's as easy as copying-and-pasting from a .csv file to .xls and creating some conditional formatting, then Leo99 is way off in his assessment in time spent. Once I got my conditional formatting set, it takes literally single-digit minutes to pour over hours of data!
I don't care about most of the run time that looks great. I care about that time I boosted a little more in 6th than I should and saw some knock as a result or specific trends in fuel trims that could indicate leaks, or a million other things that could indicate anything from sub-par fuel (bad fuel can be indicated in increased knock values, well above ghost knock and normal tip-in throttle response during too-aggressive driving for the gear you're in; all of which is imperceptible audibly) to major issues that should be quickly trouble-shot. Seriously, I would have tanks where I'd see nothing but the occasional ghost -1.4 degrees of feedback knock, but my learned knock would be 0 for the cell and DAM would be 1.0 (max); then, the next time, I'd see -2+ retard at increased load levels.
This isn't rocket surgery, folks. Once you get a system down (which is really fun to figure out and learn about,) you can see things that are out-of-whack very quickly. This isn't like staring at your coolant temp idiot gage for the first drive to see if you burped the radiator well enough or checking your O2 sensor response by watching the volt-meter cycle up and down (i.e., very little to be gleaned via these methods) - it CAN BE pretty darned informational.
//
I really hope that these apps show enough data, at a high enough resolution (1 to 10 samples per second) or else I've pretty much put my foot in my mouth, since I'd then be comparing apples (Cobb AP and AccessTunerRace software) to some Oranges (some rough Apple app.)
//
In the end, and to emphasize an earlier point: this kind of stuff IS INTERESTING AND FUN. This is the kind of thing we're on a freaking automotive forum to discuss, for crying out loud! Data from a logger will be a heckuva lot more valuable than trying to figure out what that 2 ppm Si in your UOA means!