Even if it's not full time AWD the tc is still transmitting power. It's just not engaging the front drive shaft. You still have heat and wear issues not to mention the break down of lubricants. The reason that most service intervals are time and/or mileage is that the fluids start degrading the minute the container is opened. So even if you put brand new fluid in and never use the piece of equipment the fluid will degrade over time.
If you have ever work on any type of machinery you know it's easy to tell the difference between equipment that has been properly maintained from that which has not.
After all servicing the tc is not that expensive, if you do it yourself, and it is not that difficult to do.
Jeep TC fluid costs 40 dollars a quart here so it can't be called cheap either. But I prefer to have them changed instead of paying 4000+ dollars for a new TC.
