According to Sound Devices:
4:4:4 is the biggest container available for color in video. For HD rate signals, it requires either dual-link HD-SDI (2 x 1.5 Gb/s data rate) or 3G-SDI (3 Gb/s data rate). While lower color space signals can be represented in a 4:4:4 container, when a 4:4:4 signal is sent to an input that only supports 4:2:2 color, a data mismatch results and no video is transferred.
So, when should you use 4:4:4 over 4:2:2? Read what Sound Devices has to say on the subject here.