I'm running PackageKit on Fedora 22, version 1.0.6. 

[bellet@gandi-2 ~]$ rpm -qa | grep -i PackageKit | sort
gnome-packagekit-3.16.0-1.fc22.x86_64
PackageKit-1.0.6-6.fc22.x86_64
PackageKit-cached-metadata-1.0.6-6.fc22.x86_64
PackageKit-command-not-found-1.0.6-6.fc22.x86_64
PackageKit-glib-1.0.6-6.fc22.x86_64
PackageKit-gstreamer-plugin-1.0.6-6.fc22.x86_64
PackageKit-gtk3-module-1.0.6-6.fc22.x86_64

I noticed that PackageKit downloads not only repos metadata, but also full rpm packages in the background, and saves them in /var/cache/PackageKit/metadata/<repo>/packages (maybe based on drpms)

I didn't find an option to disable this behavior, that may be undesirable in some cases :

  - when access to the network is expensive (eg prepaid access) and/or limited to a fixed amount of data, over mobile broadband for example. In such case, the user may want to choose for which usage he prefers to spend his network access.

  - when available bandwidth is slow already, the user may prefer to keep the full bandwidth available for interactive usage, instead of for background network activity, that silently reduces even more his available bandwidth.

Ideally, if everything could work automatically, the ModemManager/NetworkManager should provide a hint to other apps, if one of the connections that contribute to the default route, should be considered as "rare", and used with economy in mind. And PackageKit could use this hint to download updates more-or-less aggressively.