Rodents are similar to humans in the sense that they want to escape cold temperatures and find shelter in a warm and comfortable area. More often than not, that area will be your attic or crawl space.
Rodents are small, agile, and experts at climbing- making it easy for them to squeeze their way in to your home. Consequently, not only will your your uninvited guests proceed to chew on an endless amount of things such as your insulation, electrical wiring, and duct system, they can also transmit diseases to your family and pets.
If rodents are able to make their way into your home, this means there are existing access points which have not been addressed. Anywhere rodents can get in, air can get in too; this means there is unnecessary heat exchange between your indoor and outdoor air, which can drive up your energy bills.
Rodent proofing helps make your home less attractive to rodents and difficult to invade.