Merging brushes
Is it possible to merge multiple brushes into one? I'm asking because I'm detailing a map from the PeTI and converting it into a Wheatley-style chamber. However, the huge amount of brushes makes ~5600 visleaves, which is obviously not optimal. I do, however, need to leave them as worldbrushes.
[spoiler]WOM Test 1
Laser Cube Quest
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Not really.
This isn't quite accurate. As long as they make a flat surface, more brushes will not cut up the visleaves. Allow me to demonstrate with an example:
https://dl.dropbox.com/u/19093054/visleaf.png
Note that while the wall is made up of 32 brushes, they do not dissect the visleaf (the edges of which are highlighted in blue). If the brushes make a flat surface, meging them into one will not change the visleaf layout.
However, visleaf are split automatically, every 512 units. (Or was it 1024, I don't quite remember)
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The only way you can achieve this is by manually making brushes of the appropriate size in hammer and removing the others ones. 
And as Nacimota pointed out: they don't cut corners visleaves. The different blocks can very well be used to add some texture variation to the walls. Something like this:
Every 1024th from the map origin, along all three axes (these points are marked with orange/brown lines in Hammer).
Thanks for the informative replies. What can I do to get my visleaf count down? Or is ~5600 acceptable?
[spoiler]WOM Test 1
Laser Cube Quest
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Four Corners[/spoiler]
Depends on the size of your map.
The most efficient way to get your number of visleaves down is to use func_details.
look normal
don't split visleaves
don't seal your map
can't be dynamic
use this on all things that don't block the player's line of sight like:
* angled pannels
* Tiles on the floor and/or on the ceiling where the ceiling isn't completely blocking the line of sight in destroyed theme.
* Other things that don't block the players Line of sight.
Skip and hint brushes are your friend. There are plenty of good tutorials on the web explaining optimisation with hint and skip brushes.
Just look at Valve's light instances which you can pop in walls. They have a hint brush over it so then the vis leaf won't be cut in some odd way.