NF6X: the homebrew version is --HEAD only, meaning it pulls the latest revision of the source code from the official KiCad development branch, then automatically builds and installs it as well as, optionally, lets you migrate your library to the online github repos (causing your libraries to be always up to date) if you want to but haven’t.
Whenever a new revision of KiCad comes out, you can follow the instructions in the tap’s README.md (which is also the text of the github page) to easily update your binaries to the newer version. I don’t know how much longer it will be before official nightlies start getting made - but this lets you build your own nightly whenever you want. Additionally, this builds everything so its specifically optimized for your system and OS X version, while the binary build is built for 10.8, and It happens to work on 10.9 and 10.10 too :).
But, many homebrew formula have downloadable binaries, the reason you would use homebrew over them is the same as any other. All files are kept in /usr/local, built against local dependencies which in turn are the optimal builds for your system, and the various other things homebrew brings.
The build settings are identical to my binary releases, so I wouldn’t call it ‘switching’. The homebrew tap lets users update or build KiCad to the latest version at will, so they are not at the mercy of people like me finding enough time to update it.
It’s not just for kicad though, it can also be used for library installation with non-homebrew versions of KiCad. It’s totally interoperable, and you can have a homebrew cutting edge build installed along side my binary release, and they will share a common library. I like to think I paid attention to as many details as I could think of and make everything ‘just work’ as best I could.
But if those are reasons to try building the tap or not is up to you. I imagine there will come a point where your version right now becomes outdated enough that you want a newer one, and maybe there will be nightlies being released by then, in which case you probably have little reason to bother. If there aren’t, well you have a backup option at least