I did it two years ago, I flushed the system with a pre-cleaner and refilled with the same replacement fluid (I was testing equipment, and did not seek out this service). The precleaner, is also a seal revitalizer and meant to help condition the seals in the system. The seals can dry, crack and leak over time.
I had no discernible or noticeable difference at all! No performance gain or smoothness in the steering system.
There is no service interval for hydraulic fluid. In fact, only vehicles that have associated problems have a service interval. As many cars move towards electronic systems, there will be less of this need for this.
Power steering fluid is subjected to extreme pressure and not combustion, so it is meant too last longer. Even the power steering rack manufacturers like Dana, see no need to change this fluid unless there is a significant problem or a massive leak.
This service is basically a cash grab from a service provider, because it seems logical to change it, like all the other fluids in your car.
The equipment on the market is not very sophisticated. It consists of two hoses (one positioned higher than the other), with the lower hose sucking and the upper hose pushing in new fluid. The vehicle is started and the steering wheel is moved back and forth, while you suck and blow from the reservoir. There is no other method. You are better served to use a turkey baster and do it yourself through displacement as the system only holds 2 litres or so.
It certainly can not hurt to do so, but is not necessary and serves no real benefit's except making your car go faster, because your wallet is now relieved of the $100.00 it will cost you to do this service.