A requirement for a 2 mile CPA is common in the open ocean. Someone on this forum pointed out to me that CPA/TCPA limit (time of CPA) is better then a CPA only. This is correct. I think of this as boxing in the watch officer to limit how much risk can be taken without authorization or assistance.
One issue that can arise; in coastal waters and in heavy traffic the watch officer can avoid close CPAs by taking the ship into unsafe waters. The watch officer is not safely “boxed-in”. With paper charts the defense was to draw “no-go” areas on the chart.
The ECDIS has a better tool, the cross-track error settings. A requirement can be added to the standing/night orders that the master must be called if the watch officer plans to cross outside the ECDIS cross-track error lines. Some care is required in selecting the XTE distances for each leg.
These requirements to call the master: CPA / TCPA / XTE all tighten up watch officers decision box.