Cubemaping

[KON_Air]

Well from what I dig 16 units away from origin of props or the brush surface works best for shot that are only for them. Multiple cubemaps per room doesn't impact performance other then increased filesize but mind jumps from one cube to another... not that there are that reflective weapons (even xbow scope). Having cube maps right under/next to light sources give much better shine on surfaces... and nothing more I can think of right now.

[fug4life]

Although you can, I never really use cubemaps up close to anything unless its glass or something like water or a func_brush that is refracting (which for all I would assign the brush face anyhow). However note you can add many cubemaps per room and yes I normally tend to cubemap areas in front of my light source first, then other areas in the room. Depending on how big your room is and how many light sources you have etc. Also I sometimes add different cubemaps for light and dark areas. So it's not just one cubemap per room.

Assigning a face number to a cubemap is helpful to make sure a certain face gets lit.
For instance if you have say a funcdoor that lifts up vertically the face that is on the bottom of the door is dark, you can pick a cubemap from a lighter area of the map and assign that face number to it. (A fix for one of my maps, I've got on my to do list).

And like KON_air said run around with the crossbow and you'll see the reflection of the scope 'pop' from one cubemap to the other.

And a trick I learnt from PowerMad (god bless him) that Valve never seem to do. Is kill your sprites from the world before you build cubemaps.
to do this I normally

sv_cheats 1
god
noclip
picker
ent_fire !picker kill

(just make sure you got the red/green/blue axis on the correct sprite and not some other world ent).

Then buildcubemaps how you would normally, the sprites should be killed even after switching ldr to hdr or w/e just double check.

I do this for a much more realistic effect that way sprites from halfway across your map around corners etc aren't reflecting infont of you as you run around.