Motion sync technology ensures that the mouse is sending sensor information to your computer at the same rate its asking for mouse position data.
You can think of it like Gsync or Freesync VRR but for mouse movements.
The end result of effective motion sync should be more accurate and smoother mouse movements.
Does motion sync add latency
According to Pulsar, motion sync will add a unperceivable 1ms delay to tracking data. Razer mice has motion sync turned on by default and does not have an option to turn it off, meaning the latency is good enough to not be noticeable.
Does motion sync affect battery life
Motion sync should have negligible effect on battery life. There are reports of the Pulsar X2 Mini battery suffering with motion sync on, but I think that’s just a bug on Pulsar mice.
The flagship Razer mice all have motion sync on and their battery life is quite good.
Should I use motion sync
The impact motion sync is minor, but there is very little downside from having it on. You will likely get better feeling tracking with motion sync on.