Checked with version: 2017.4
Minimizing motion-to-photon latency is the key to giving the user the impression of presence; a term used to express the feeling of being physically connected to the experience one is living in virtual reality. It is recommended to target 20 milliseconds or less motion-to-photon latency for any input made via VR hardware to be reflected on the HMD’s screen. This includes the handling of HMD rotation and position as well as VR controller rotation and position.
Avoid handling input in FixedUpdate as this callback does not necessarily get called once per frame (depending on Time Settings and performance) and may incur increased input latency.
Tracked poses may potentially be handled twice, once in Update() and again in onBeforeRender(). Any additional handling that occurs in onBeforeRender() should be very lightweight or can result in serious input latency.