The first type of compile is the quick compile. If your level is under heavy construction, hasnít been sealed and you only want to look at a few changes you made entities or brushes, this is the type of compile to do. In this case, you only care that geometry is built so that you can look around. You must set CSG, and BSP. You can also, take some lag out by using a Fast VIS, but leaving VIS unchecked is good in most cases.
The second compile is a more thorough (although not full) compile. This is used when you want to check the read speeds (R_SPEEDS) but donít care about lighting. Set the BSP, CSG, and VIS to run, but also check the Full VIS box. This compile would take longer to build your map, but will have the proper VIS Matrix. Full VIS can also fix some brush errors, though some can still seep through VIS.
Next is the full compile. Check all the options in the normal compile, but also, check the RAD, and the Extra RAD check box as well. This is the most time consuming compile of the lot, but also fixes many bugs, also adds all your lights.
Its always a good idea to restart your computer before tempting a normal, or full compile, because the more RAM that is free, the faster your compile will run.
The Swap File can make compiles run at 1 /2 speed making your total compile time double. So the faster your computer, and the more RAM You have can speed your compile times up.
Once you actually run the compiler, the dialog will change to a log window and a display of progress bars showing compile progress. If you read the log window you can learn a lot about how the level is being handled.