On what occassion would that be used, Ajax validation?

So say two dropdown boxes, two input fields, any custom field. I would be using it for eg, the following:

Enable this plugin for the following blogs:
Blogs [ textbox ] to [ textbox ] [ inclusive or exclusive ] [ include or exclude ] [ add another group ]

And then I would save the variable as a exported array generated from the values of those fields. So $Settings->set('blogs', serialize($array));