Windshield Repair is a process that restores strength and
improved visibility to a windshield that has been damaged, usually
by a rock. Most repairs performed by a qualified repair technician
will result in 80% -95% improvement in visibility depending on the
initial damage. Professional repairmen use high quality equipment
capable of removing air in the damaged area and replacing it with a
high quality glass resin that will prevent further damage and improve
the finished look of the repair.  Most companies usually will guarantee
their repairs for a minimum of one year with many giving a lifetime
guarantee.
Examples below provided  by Glas-Weld Systems.®   

Windshields and safety glass are made from a "sandwich" of plastic
laminate between two layers of glass. An impact strong enough to
damage the hard  outer layer can cause an infinite variety of chips,
cracks, crescents, stars, or combination breaks. Often, the imperfection
is tiny at the surface and expands into the familiar bulls-eye shape as it
spreads toward the center layer. Most  insurance companies will waive
your deductible and pay for your repair.  They do this to help avoid costly
replacement of your windshield should the damaged area spread to the
point where repair is not recommended.