Mad Baron,
What is going on here is ekrommen has installed a mod whereby the original ground textures have been swapped with ones with a grid pattern.
The grid can easily show you the 20m squares, and as you can see, there is a big color difference in hexes of different height... From Low Black Hexes, to High White Hexes.
I would guess he downloaded the mods from here:
http://www.cmmods.com/
It's really a matter of personal choice. I personally like to fly over the battlefield, soaking up all LOS possibilities, so I don't think I would benefit all that much from a grid mod. I play CM as if it where a 3rd Person Shooter. I like the eye candy, and am a decent enough player without the grid.
But if you're the type of player who plays CM like a boardgame: from top down, or a very wide view like the screen shot above, then the grid and the large color difference in different height hexes may help alot.
If you ever said... "I though my Goddamn tank was hidden! after watching it brew up behind a slight crest that you though was a huge mountain blocking all enemy LOS, then maybe the grid mod is for you.
Consider it.