For that matter, why isn't CompizConfig installed by default? So much stuff is hidden in there and it's impossible to discover without running across someone talking about it online. This is exactly the sort of thing that should be on the menu by default as "advanced compiz settings" or something like that.
On the other hand, discoverabiliy is still a big issue with Unity in general.
1. Open CompizConfig Settings Manager (if not installed, `sudo apt install compizconfig-settings-manager`)
2. Click the "Ubuntu Unity Plugin" plugin
3. At the bottom, "Enable Low Graphics Mode"
4? Restart Unity / reboot (? because I'm not sure it's necessary. See for yourself :)
Agree it would be neat to surface the option in the regular System Settings panel, though.
Source: http://www.omgubuntu.co.uk/2016/11/enable-low-graphics-mode-...