About front windscreen lamination, during a mishap, the windscreen tends to shatter, and this can spell disaster for those sitting inside. By laminating the front windscreen (3M or Garware), when there is a mishap, the windscreen cracks but is held together by the lamination.
Automotive windshields are already laminated with a plastic layer in between two (or more) glass layers from the car manufacturers itself. When the windshield cracks, it prevents the glass from forming sharp edges. If you notice a cracked windshield, it usually looks like a spider web.
If you leave it unattended, the crack will spread due to heat, wind speed etc and lose its strength to hold together the glass pieces in tact. Hence it is always advised to get your windshield changed if you have a crack asap.
What these sunfilms for the front windshield do is make you car look cool (specially if you have a gf ) and to a certain extent filter out the IR and UV rays.
Though in doing so, they create another problem. At night they also reduce visibility on the highways.
PS: Remember in the older days, people used to put a black sticker on the top 2" of the windshield? Now if you notice most cars come with a tint at the top layer of the windshield which is in a different colour to the rest of the windshield as OE itself.