In most Mentor Graphics PCB releases, the MSVC++ Redistributable software is installed every time you install software. It's useful in the cases where you install new releases, but its not always necessary when re-installing the same release or applying updates.
Setting the environment variable SDD_SKIPCORECOMP=1 before installation prevents the installation of these packages, and can save you a bit of time during installation. It's especially useful when you are installing a source tree for client/server installation on Windows. If the server is not used to run the applications, there is no need for the SDD core components.
Use this with caution! It will prevent the packages from being installed in if set, and you do need those packages to run the applications or if you are re-installing to repair a corrupted software installation.