Since even Extended Life transmission fluids can lose their effectiveness prematurely, changing your fluid as needed or every 3 years or 36,000 miles may prove more effective and economical in the long run. Running with old or an insufficient levels of transmission fluid can cause the transmission to work harder, transferring engine power less effectively. This can cause a substantial decrease in fuel efficiency.
Having your transmission fluid serviced regularly can extend the life of your transmission and prevent a transmission rebuild or complete replacement which could cost $2500 or more. From a Safety standpoint if your transmission is unable to shift reliably or shifts erratically you can endanger yourself or other motorists. And, although it may not have a high environmental impact, leaking fluids are harmful to children, pets and other animals.