Maintenance schedule

According to my owner's manual, it recommends specific intervals for maintenance of my vehicle. It lists each element as either needing maintenance every 12 months or after x amount of miles, whichever comes first.

Is it really necessary to perform maintenance according to the time interval if the miles haven't been accumulated yet? I'm curious to know how time affects different fluids (oil, transmission fluid, engine coolant, etc.), spark plugs, air filter, and other things.