Advantage of Windows Installer service.

1. Windows Installer Service
Windows installer is a service, which is developed by Microsoft for installing and
managing applications. The Windows Installer is an engine for the installation,
maintenance, and removal of software on modern Microsoft Windows systems. The
installation information, and the files themselves, are packaged in installation packages,
commonly known as "MSI files", from their default file extension. The process of
creating MSI file is some time refers as application repackaging.
Prior to Windows Installer, software applications used various setup
technologies, each of which contained unique installation rules for each application. At
times, the applications did the wrong things at setup time. For instance, an earlier
version of a particular file might be installed over a newer version of that same file.
Some setup technologies made it difficult to maintain accurate reference counts on
shared components for the many applications installed on a computer. As a result,
installing or removing certain applications might break other applications.
Some of the disadvantages of setup.exe are as follows:
1) Setup.exe (legacy installer) does not contain any central reference for
installation rules, because setup was not considered to be a part of the
development process.
2) Legacy installer rarely maintained shared dynamic link library (dll) reference
count. As a result installation or removal of a given application often broke
existing application on computer.
3) These legacy installer treats file, registry and other resources as a disjointed
collections.
4) Legacy setup doesn’t support repair functionality of the application.
5) Maintenance cost of the legacy setup is high and these can’t be deployed on
the machine easily. Lots of administrative effort is required to install these
legacy setups.
The main reason for creating msi is to create a consistent and customized,
installation. The main benefit of creating a consistent, customized installation is to
reduce desktop support costs.

2. Repackaging of an application to msi seeks to eliminate these types of issues
through “customized consistency”. Customized consistency means customizing, or
repackaging, an installation so that it behaves in a manner consistent with the
company’s standards. Adherence to standards means that end user desktops are easier
to support because the system administrator knows the software installed on them
conforms to predefined standards that, in turn, reduce support costs.
Some advantages of creating MSI are:
1) This technology creates reliable packages that can be successfully distributed
through an organization through SMS server (System management Server).
2) Provide consistent and reliable version rules.
3) Provide Advertisement: The installer registers the application, creates
shortcuts and menu entries, associates file types etc. without actually
copying the application files to the user's hard drive. If the user or another
application tries to access the advertised program, it is installed on demand.
In this case, the invoking of the installer is handled by the operating system.
4) Provides installation on Demand: This is quite similar to Advertising.
However, it doesn't refer to a whole application, but to a feature or function
that is called from inside the application. When the application tries to access
the feature and finds that it isn't present, it calls the installer service to install
it just in time. These way users don’t have to anticipate the functionality they
need before they ever used the product.
5) Rollback: The installer records all changes it makes to the system, and
creates temporary backup copies of overwritten and removed files. If setup is
aborted, the system is reverted to its previous state. After the setup is
finished successfully, the rollback information and backup files are deleted to
save disk space.