This method is quite different from the other two. It could be thought of as a specialised method which should only be used if you need the advantages that it provides. Instead of giving the element a single value it provides an array of values where each item in the array corresponds to a sample of audio in your buffer. There are a couple of reasons why this might be useful.
Certain optimisations may be possible since you can iterate over your dparams array and your buffer data together.
Some dparams may be able to interpolate changing values at the sample rate. This would allow the array to contain very smoothly changing values which may be required for the stability and quality of some DSP algorithms.
The array method is currently the least mature of the three methods and is not yet ready to be used in elements, but plugin writers should be aware of its existance for the future.