The Light List (LL) is a crucial USCG publication for navigation for several reasons. The primary one is it includes information about the aids to navigation (ATONs, ie buoys, lights, day marks, radio aids) that is often not available on nautical charts, such as the nominal range and height of some lights, and other descriptions. This is especially true when relying on paper charts or using echarts in the RNC format, which are just graphic images of the paper charts.
A partial exception comes into play when using official US vector echarts (ENC) as these charts do include ATON data that are updated when the charts are updated, so in principle with automated ENC updates, you have all the latest ATON information as of about 10 days. They are updated every week, with about a 3 day processing time. Thus an updated US ENC is much like having the latest Light List on board—but we are then at the mercy of our echart program that we count on to alert us that a new edition is available.