When a person is a lead in SFDC, they have a lot of company-level data associated to them, like number of employees and address information. When those leads convert to contacts, some people believe that you should stop updating any company-related details on the contact, because it leads to data disparity. Now that sounds better in theory than practice. For example, if someone works remotely in Arizona for a company headquartered in New York, and you are an event coordinator in charge of inviting people in AZ to an event, would you rather have EVERYONE who works for the NY company with NY in "State" on their record, or AZ? You could certainly argue AZ on the person, would be better.
However, if you think about a field like "Number of Employees" having 1-10 on a person's record, because that's what they selected on a form, while the account has 5000-10000, makes a lot less sense.
Ultimately, I'd advise to consider FIELD-LEVEL read/write access, opposed to OBJECT-LEVEL restrictions.