Caveat: Some additional work is needed to get reduced input lag for VSYNC ON. Large Vertical Totals can produce reduced "VSYNC ON" input lag when used in conjunction with RTSS scan-line frame capping. You need Direct3D Present() and OpenGL glutSwapBuffers() to occur near the end of VBI (instead of beginning of VBI). This allow games that use smart inputdelay techniques (intelligently elayed input reads to as close timing as frame presentation) to gain reduced input lag.
Essentially this is like the HDMI Forum's "Quick Frame Transport" -- in a Roll-Your-Own Hack.
In summary, the advanced Large Vertical Total trick has several benefits:
Strobing Modes -- Yes, can reduces the double-image effect -- aka reduced strobe crosstalk -- on blur reduced monitors. Only on monitors capable of synchronizing panel scanout to cable scanout (e.g. BenQ XL2720Z). This is explained at
http://www.blurbusters.com/crosstalk .... Basically a faster LCD scanout followed by longer pauses between refresh cycles. This allows more time for LCD pixel transitions to complete on the whole screen surface before flashing the backlight on a fully-refreshed panel. The more a faster-GtG is hidden in a long VBI between refresh cycles, the more CRT motion-clarity (no-double-image-effect) that an LCD panel can become. Be warned, some monitors already scan-convert internally, and thus, Large Vertical Total may not be able to speed up the scanout on those monitors, and does not reduce strobe crosstalk on all models.
Low Hz on High Hz Monitors -- Using Large Vertical Totals can reduce the lag of 60Hz gaming on 240Hz monitors, since some 240Hz monitors are stuck scanning their panels at full 240Hz velocity. Using Large Vertical Total (e.g. VT4400+ for a 60Hz signal) on a 240Hz FreeSync monitor, can produce a fixed-60Hz non-VRR mode that is much lower lag than a common 60Hz signal.
VSYNC ON -- Yes, when combined with RTSS new Scan Line frame capping feature (combined with VSYNC OFF) to emulate "HDMI Quick Frame Transport (QFT)" in software synchronized frame flipping. This is to flip frames near end of VBI instad of Window's default Present() timing at beginning of VBI during VSYNC ON. Delaying the pageflip allows inputdelay logic to get input reads closer to photons-hitting-eyeballs time. Flipping early in a long VBI means a long wait before the frame finally becomes displayed into photons.
VSYNC OFF -- There is no known latency benefit to using Large Vertical Total tricks on VSYNC OFF modes. This is because in unsynchronized framerates outputting willy-nilly, it all averages out to be the same lag at the end of the day. If you're using a non-strobed VSYNC OFF mode, and don't have a need for scanout-velocity compensation (e.g. speeding up cable scanout to match native panel scanout to avoid linebuffering lag) -- then don't bother worrying about Large Vertical Totals.
It's certainly a Pandora's Box of complexity that no other websites (other than Blur Busters) is able to explain. But it's massive lag reductions for a 240Hz monitor being forced to display at only 60Hz -- up to 12ms less input lag for top-edge -- to the point where I wish XBox/PlayStations supported Large Vertical Totals when connected to today's 240Hz monitors. Since this is a PC-only trick, that requires a Custom Resolution Utility, in order to utilize.