b30GrassVS is believed to be unused by the game. It possibly toggles shader model 3.0 grass vertex shader. In testing, there was no apparent difference between setting it on or off. Since Skyrim requires use of shader model 3.0, it probably is disabled.
Default is 0. Low and Medium are 0. High and Ultra presets are 1.
fGrassMaxStartFadeDistance sets the maximum distance that Grass Fade (fGrassStartFadeDistance) can be set to in the in-game Settings > Display menu. It appears to have no actual effect.
Default is 7000.
fGrassMinStartFadeDistance sets the minimum distance that Grass Fade (fGrassStartFadeDistance) can be set to in the in-game Settings > Display menu. Unlike fGrassMaxStartFadeDistance, setting this too high will remove grass starting from the area farthest from the player and working inward, removing all grass if fGrassMinStartFadeDistance equals fGrassStartFadeDistance. Negative values cause a tiny patch of grass to be shown around the player even if fGrassStartFadeDistance is set to 0. It is recommended to be set to 0.
Default is 400.
fGrassStartFadeDistance sets the distance grass will begin to fade. It is changeable in the in-game Settings > Display menu as Grass Fade.
Default is 3500. Low is 0. Medium is 3000. High is 5000. Ultra is 7000.