OK, here's the situation...
A few weeks ago a friend asked me about the kind of GPS / heart rate monitor I was using, and I sent him a fairly long email about my choice of the Garmin Edge 705, its suitability for biking but not for other things (I think he's looking for something to use with running), and why I went with the 705 rather than the newer Edge 800. My reason: "I went with the 705 because its data files are basically XML while the 800 uses binary files."
What that means is that the 705 produces output that is basically alphanumeric text, readable/editable by any text editor or word processor. Granted, the text is a bit hard to follow, but the basic idea is just a version of extensible markup language, like:
here's the data
here's more data
It's structured almost like an outline, except instead of numbers and letters for headings and subheadings, there are named "tags" like <Track> and <HeartRateBPM> and <Location>. A little bit of patience and you can find your way around most XML-based files, and there are also may programs and tools that recognize XML and can work with it as structured data.
By contrast, the (binary) file created by the Edge 800 is something that isn't in any human-readable format: it's just a bunch of ones and zeroes, meant to be read and understood only by specially designed programs. (Other examples of binary files would be things like image files, or MP3 music files.) In other words, I couldn't just fire up a word processor and look at my ride data, and -- more to the point -- I couldn't put together my own simple programs to find or extract data from the files, at least not easily.
This decision, to go with the text-using 705 rather than the binary-file 800, was one I made a few years ago, when I needed to replace an earlier Edge 705 that I'd lost on a ride. Partly it was because I would be getting an exact replacement of what I'd already had, but my main reasoning was ideological, as in "Information wants to be free!" I wanted to see my data without anyone's help.
After writing my friend though, I got to thinking about my decision, and realized that my reasoning really didn't carry much weight: after one or two experiments, I almost never actually looked inside my data files, or analyzed them with my own home-made programs. I would upload my ride data to the Garmin site, or use standard training software like everybody else. Being able to "look under the hood" of my data files was a nice option, but I no longer had the desire, or need, to actually do it.
Anne and I did a road ride a week ago on Saturday, and for some reason the Garmin website wouldn't recognize the data, and neither did any of the training software. Uh-oh. I Googled the problem and found out that sometimes the Edge 705 doesn't correctly record certain pieces of data, and so one of individual data records was screwed up and the file was "corrupt." The solution is easy: just remove the offending record -- you'd lose one second or so of ride data, but otherwise the file would be as good as new. I opened up the file in Emacs, found and removed the offending record, and things worked fine from then on. So OK, maybe it is useful! -- though it would be even more useful if the 705 didn't create corrupt files.
Since I've had the "new" Edge 705 for a few years now, and since I also have a spare, after someone found and returned the one I'd lost, the question was mostly academic, but we did a ride yesterday in Jim Thorpe on some rocky, overgrown trails (we did Green Blaze), and my Garmin popped out of its mount somewhere along the way. When I noticed it was gone I considered going back to look for it, but it could have been anywhere, under rocks or in the brush, at any point along a 10 mile section of trail, so forget it man, it's gone. So, now I'm down to the spare GPS and a handlebar mount that I no longer trust -- and the Edge 800, and the even newer Edge 810, both have a better mount -- and binary file be damned, I think it's time for an upgrade, especially since they stopped making the 705.
"Chi Wên Tzu used to think thrice before acting. The Master hearing of it said, Twice is quite enough." -- The Analects