The benefit is that Homebrew uses what you already have in the system, without creating its own separate world where it rebuilds everything even if a perfectly working version is already provided.
MacPorts used to do this, and then stopped because the copy on the system sometimes wasn't "a perfectly working version" and by virtue of being tied to an entire OS update caused giant incompatibilities (as you had to deal with, simultaneously, broken old versions and broken new versions existing in the ecosystem).
Well, either those are corner cases or the Homebrew guys are doing a great job because I've never had a problem. Not a heavy user though. Before Homebrew I used to build my own packages because I tried and couldn't stand Fink or MacPorts.
I think Homebrew has been around for about two years now; it came out during the Mac OS 10.5 era. That means that only last week has it even gone through a second major release of the OS.
MacPorts, formally DarwinPorts, has been around for nine years, and has been post-1.0 for the last six. I am pretty certain that it came out during the Mac OS 10.1 era, and at the time supported down to 10.0.
Given this stark contrast, to compare the compatibility complexity experience of MacPorts to Homebrew with the statement "I've never had a problem" is nothing less than hubris.
Seriously, the history of every package management system (including such stalwarts as RPM, APT, MacPorts, and even rubygems) is the same: they start off with the attitude "why is this so complex" and then get to find out over the next decade exactly why those things are so complex.
Honestly: why does it matter oh so very much to everyone that you have to rebuild a few more packages? Isn't this just a problem of not having binary packages? If so, rather than sit around and build Homebrew, someone should have just contributed some bandwidth back to Fink.
