According to the report, this will allow firms to make final recruitment decisions after they have a better idea of their year end finances and can more properly asses firm needs for the following year. It will also allow for a better recruitment process than the current one, which is essentially based on a twenty minute interview and a follow up phone call.
The NALP rules are voluntary and there is no official enforcement, but firms that try to circumvent the rules may find themselves banned from doing on campus recruitment at one or more schools. This happened last year when Harvard threatened to ban Sullivan & Cromwell from future recruitment events after S&C wanted students to respond to offers within 14 days instead of the NALP recommended 45 day window.