The core rulebook states:

"For every degree of success achieved, add +10 any Navigation (Warp) skill tests for this voyage, whilst for every degree of failure a -10 modifier is imposed instead."

In the original rules this only applies to the Steering the Vessel part of navigation. The errata however changes both Charting the Course and Leaving the Warp to Navigation (warp) checks as well. Does that mean the player should apply this bonus or penalty to these checks as well?

We are following the errata, and use the modifier for every navigation (warp) roll. This makes quite a lot of sense, as it explains why the limit of the Astronomican is a natural limit for Imperial expansion.

Friedrich van Riebeeck, Navigator Primus, Heart of the Void