Precompiling files can reduce compilation times, resulting in faster edit, compile, link, and debug cycles.
The general idea is to precompile header and implementation files that do not change and reuse the compiled code, instead of recompiling the same files
for each source code module in the project.
The ATL COM AppWizard automatically sets up precompiling of the standard ATL files by designating file StdAfx.cpp to be precompiled through file StdAfx.h.
This produces a precompiled header file (*.pch) using the project name, for example, PhBook.pch.
See the Visual C++ documentation for more details.