Without it, when building with --dbg=on --opt=off on Windows we get some object files, which exceed the maximum object size of the VC++ compiler.
See this article for more information.
E:\workspace\mongo>scons -j 12 --dbg=on --opt=off --ssl --dynamic-windows --win-version-min=ws08r2 CPPPATH="D:/workspace/libs/snmp/include D:/workspace/libs/sasl/include D:/workspace/libs/openssl/include" LIBPATH="D:/workspace/libs/snmp/lib D:/workspace/libs/sasl/lib D:/workspace/libs/openssl/lib" --mute build\debug\mongo\s\catalog\dist_lock_catalog_impl_test.exe scons: Reading SConscript files ... scons version: 2.3.4 python version: 2 7 6 'final' 0 Checking whether the C++ compiler works... (cached) yes Checking whether the C compiler works... (cached) yes Checking if C++ compiler "$CC" is MSVC... (cached) yes Checking if C compiler "cl" is MSVC... (cached) yes Detected a x86_64 processor Checking if target OS windows is supported by the toolchain (cached) yes adding module: subscription Checking if C compiler is Microsoft Visual Studio 2013 Update 4 or newer...(cached) yes Checking if C++ compiler is Microsoft Visual Studio 2013 Update 4 or newer...(cached) yes Checking if we are using libstdc++... (cached) no Checking for C++11... (cached) yes Checking Windows SDK is 8.1 or newer... (cached) yes Checking if we are on a POSIX system... (cached) no Checking for storage class thread_local (cached) no Checking for storage class __thread (cached) no Checking for storage class __declspec(thread) (cached) yes Checking for C++11 is_trivially_copyable support... (cached) yes Checking for C++14 std::make_unique support... (cached) yes Checking for C++ header file execinfo.h... (cached) no Checking for C library pcap... (cached) no Checking for C library wpcap... (cached) no Checking if std::atomic<int64_t> works... (cached) yes Checking if std::atomic<uint64_t> works... (cached) yes Checking if std::atomic<int32_t> works... (cached) yes Checking if std::atomic<uint32_t> works... (cached) yes configuring module: subscription Checking for C++ header file net-snmp/net-snmp-config.h... (cached) yes Checking for sasl_version_info(0, 0, 0, 0, 0, 0) in C library sasl2... (cached) yes Checking for C library gssapi_krb5... (cached) no Checking if OpenSSL is available...(cached) yes Checking whether FIPS_mode_set is declared... (cached) yes Checking if __malloc_hook is declared volatile... (cached) yes scons: done reading SConscript files. scons: Building targets ... Compiling build\debug\mongo\s\catalog\dist_lock_catalog_impl_test.obj dist_lock_catalog_impl_test.cpp E:\workspace\mongo\src\mongo\s\catalog\dist_lock_catalog_impl_test.cpp : fatal error C1128: number of sections exceeded object file format limit : compile with /bigobj scons: *** [build\debug\mongo\s\catalog\dist_lock_catalog_impl_test.obj] Error 1 scons: building terminated because of errors.