As far as I can tell from his post, BruceL is simply moving the package cache (where the App Manager and apt-get temporarily store downloaded packages) to a partition with more space, and then symlinking it back, so it appears to be in the same place. This will (apparently) allow you to install build-essential without running out of room during the download step, however, it doesn't fix the problem of un-optified packages eating up your rootfs space once installed.