[Jach]

Space is time.

From the Gentoo wiki: -Os is very useful for large applications, like Firefox, as it will reduce load time, memory usage, cache misses, disk usage etc. Code compiled with -Os can be faster than -O2 or -O3 because of this. It's also recommended for older computers with a low amount of RAM, disk space or cache on the CPU. But beware that -Os is not as well tested as -O2 and might trigger compiler bugs.

I believe Apple compiles (a lot or all?) of their stuff with -Os.

Anyway C++ exceptions are awful. ;)