There are three types of automatic transmission services: flush, pan removal, or both. In our opinion, pan removal is the best option in both cost
Another benefit from routinely servicing your vehicle is the overall inspection of the drive train. Inspection can find problems before they are apparent while driving. Repairing a problem before drivability is compromised will lead to the best performance and durability of your vehicle.
The question asked most often is about how much fluid is removed in each service. Flushing in some applications removes more of the old fluid, whereas pan removal and torque converter draining does so in others.
The key part to service is not all about the fluid but rather the cleaning out of the normal debris in the pan and on the magnet in the pan, and the cleaning or replacement of the filter. Transmission fluid does not get contaminated like engine oil with antifreeze and combustion gasses. It is just transmission fluid. That is why transmission fluid does not need to be changed as often as engine oil.
In fact, the fluid used in most vehicles is capable of running 100,000 miles. The lubricity does not change much but the color will. The color is just a pigment, which over time will change from the heat normally created in transmissions.
By routinely servicing your transmission, you do several things. With the tight tolerances and internal electronics in today's automatic transmissions, normal debris accumulation can cause subtle changes in the operation of your transmission, which over time could cause a failure.
Some of the internal transmission electronics are magnets when energized, so they are prone to plugging with this normal debris. There are filters and magnets in transmissions, which are designed to catch this debris when changed and cleaned on a regular basis.