G-Sync: Low Latency Mode (On or Ultra) - Best Setting?

Hello,

I've got my machine all set up for G-Sync, I read through the Blur Busters article a while ago, I got the calculation for proper refresh rate ((Refresh - (Refresh x Refresh/4096) = Max Frame Rate). That's all well and good. But I've never quite understood "Low Latency Mode".

What's the best setting to use? I am in a situation where I am CPU bottlenecked, so I would appreciate some guidance there. I think "ON" is probably the best, as my understanding is that it controls the frame buffer, but I'd appreciate some input. Thanks.