If..... frequent towing, or mountain low speed driving (off road). Normal driving results are 1st change around 15k miles, and then about every 30k miles after that.
The DPSF fluid is easy to change on the PP and it's inexpensive. Considering it's sophisticated design it's cheap insurance. As a low mileage driver I still do it every other year.
Normal driving requirements are more reasonable: 1st change around 15k miles, and then about every 30k miles after that. That said, if you do towing and off-roading a lot, perhaps it's better to find a reasonably priced mechanic or learn how to do it yourself.