I am unsure if I am doing this right and I am sure there are many ways to do it.

I have a scene made up of 38 standard terrains of varying sizes and tons of models too.

My scene is something ridiculous like 300,000,000,000 polygons..... may have too many o's! but you get the idea.

I decided to put procedral mapping on a terrain, increased the resolution and then baked to it to a smaller polycount ....about 30,000 polys rather than 1,000,000. The results looked great much better than it looked as a standard terrain but with far less polys. 

 I found the option for decimating polys but the quality seems to get lowered doing it that way. The way I am doing it seems as if I am getting better quality terrain by reducing the polgon count. rendering is quicker and looks better.

Is there any disadvantages doing it this way ?

I am surprised at the results and I am sure there must be a catch ;-)

Correction -  300,000,000 polygon scene!

Good materials will hide poor polygon modeling when the camera is not all that close to see the polygons.

Yes I have realised this now some of my terrains look really good, but some I tried last night look really poor and it was down to the materials. Looks like I have my answer.

 how are you reducing the polygons without decimating?
love esther

estherau - he probably meant, he generated a procedural terrain, raised the terrain resolution in the terrain editor, then selected the terrain in the world browser list, right-click on it to get menu and chose 'bake to polygons' order.
Then a window opens with a slider and polygon count info - there you can control higher or lower amounts of vertices and polygons ...

 i see

Yep thats what I did ! Still having some good results and some bad!

The results have to differ for each varying kind of terrain, because of it's geometry, shape and polygon count and therefore the right amount of polygon decrease has to be figured out by trial and error ...

LangDetectru>de GoogleC

Reduzierung