External SSD Array, Why?

What is the purpose of an external SSD Array, via TB2? By this I mean, if you already have an SSD in your computer, what is the advantage of adding (2-4) more externally?

Is this configuration primarily for video? If the answer includes, "it processes things faster." My follow up question would be, "how is having an external SSD faster than the internal one the MP comes with?"

In short, I need the idiot's guide to advantages of having an external SSD array. Or, if you're having problem xxxx, an SSD array will help considerably.

Thank you for your help.

1tb

Ok, so I have the 1TB SSD drive in my MP. What I used to do was load all of my images (and small amount of video) directly off the card and onto external HDs (via TB2). Then I would work with them from there. What I've started doing is loading the data directly onto the SSD-HD, perform the initial work, then push it out to the external HDs (back-ups etc). The only thing I keep on my SSD-HD are applications. Everything runs smoothly.

What I'm trying to understand is at what point (if it can be made) would putting the data on an external array of SSDs make the process above faster?

FYI - each RAW image is approx 32MB.

Again, thank you