I was on the phone with someone yesterday that has a number of distributed Macs in offices with low bandwidth. So they need to control when updates are downloaded and installed because they can fail or cause issues with other systems when they download automatically.
This option is great for home use but can be challenging in larger environments. So it can be disabled with the following command, which creates an AutomaticDownload key in the com.apple.SoftwareUpdate defaults domain and sets it to FALSE:
sudo defaults write /Library/Preferences/com.apple.SoftwareUpdate AutomaticDownload -boolean FALSE
Once machines return to areas with better bandwidth or this isn’t a need it can then be re-enabled by using the following command:
sudo defaults write /Library/Preferences/com.apple.SoftwareUpdate AutomaticDownload -boolean TRUE
