You may have noticed additional Stage 3 links marked with "desktop profile" on the Gentoo downloads page recently. So what's this about?
The only difference between a "normal" Stage 3 file and a "desktop profile" Stage 3 file is that the latter has a desktop profile selected (surprise!). As example, if a "normal" amd64 (x86-64) systemd stage uses as profile setting default/linux/amd64/17.1/systemd, then the "desktop profile" stage uses
default/linux/amd64/17.1/desktop/systemd. The packages in the @system set are exactly the same, however, in the desktop profile more use-flags are enabled, which means many additional dependencies are merged.
This leads us to the point of the "desktop profile" stages: if you do a desktop installation (for anything from KDE to Gnome or XFCE), these files give you less initial rebuilds and compiles, at the cost of a larger download. And that's all.