VAFC allows you to trim/add fuel at specific points (RPM). This is helpful, b/c most Hondas run overly rich at WOT, and with the VAFC and wideband o2, you can trim out fuel to reach the ideal A/F ratio for maximum power/effienciency.

Also, it allows you to move your VTEC point to the optimum place depending on your mods, thus removing the "dip" before VTEC x-over that usually happens.

I gained ~20whp in the midrange and ~7whp peak just tuning the VAFC on my I/H/E modded R.