How often you service your fluid is dependent on how you drive your rig. If it's a flat-lander grocery-getter, the fluid could literally last 100k miles. But, if you drive at all in the mountains, the life of the fluid goes way down due to the temps you'll be attaining climbing grades. As the temperature of the fluid goes up, the effective life expectancy of the fluid goes down.
For people like myself who do drive in the mountains and go on 4wheeling trips, I believe a complete renewal of the fluid should happen every 30k miles. But, instead of renewing the whole capacity at one time, I choose to do a drain and refill every other engine oil change, which comes out to a drain and refill about every 10k miles since I perform engine oil changes every 5k mile intervals. Drain and refills are a dilution process (adding new fluid to old fluid), but it works really well to keep your fluid in good shape.
There is no need to drop the pan on these transmissions unless you're just curious about the health of your transmission because you bought the rig used or your fluid was really black and in bad shape and you suspect the filter might be blocked up with deposits. A transmission that has been taken care of will not build up significant deposits to block up the fine mesh metal filter media in the filter. I've cut one apart, and the media was probably around 95% unblocked. So, for those taking the time to drop the pan to clean the magnets and replace the filter, I do believe you're wasting time and money.
A thing to do to guarantee you'll never have to worry about the trans filter becoming clogged, is put a Magnefine in-line filter in the trans cooler return line. Those filters are rated to last 30k miles. I replace them every 20k and it's a hell of a lot simpler than going through the pains of dropping the pan and cleaning off old FIPG off the pan and transmission.