These two videos should help teach anyone how to use occlusion blocks:
http://www.youtube.com/watch?v=Q5QISWQuSDI (basics tutorial)
http://www.youtube.com/watch?v=3lDi0p0Gkuw (advanced tutorial)
Occlusion blocks can be very effective when used right but they can also be counter productive.
Occlusion blocks themselves require memory and although each one is only 8 points, put 500 in your map and that's 4000 points!
The important thing to remember when deciding where to place them is that they will only block what the player is looking at. For example: Lets say you have a two story building, each floor loaded with detail, you could place an occlusion block between the two floors but a player on the bottom floor would have to be looking at the ceiling or a player on the top floor would have to be looking at the floor to gain any benefit from it.
An example of good use of an occlusion block would be if, lets say, you had a tall concrete wall and on the other side you had a base with lots of detail, trees etc. A player running at the wall towards the base is unable to see the base behind(because of the wall obviously) but the PS3, not recognising a concrete walls ability to block someones view, will load it anyway because it assumes the base is in the players view. Place an occlusion block in the wall and the base won't be loaded for that player.
Hope this helps.
