Data that is often used includes evaluations of employee personal characteristics such as level of risk taking, leadership aptitude, conscientiousness, orientation toward quality, engagement, and attitudes toward coworkers.
In some cases, the lawyer can negotiate a carve-out of certain information that is valuable to the employee (e.g. performance evaluations) so it can be used in future employment or business.
Rather, their responsibility may be relatively minor: asking and collecting these evaluations from the working peers of a given employee, and then doing a write up of what they find.