From a customers point of view... we provide a system by which you can receive and review your legal bills in one place (instead of dealing with PDF's and paper invoices). Then you can approve them, mark them up, and pay them.
In the background we provide categorization of line items, insights into what they mean, if the they trigger any guideline flags / questionable charges. As far as how that happens technically... well, that's our secret sauce. Can't divulge it.