Thank you for your question. We provide a description of these mesh setting in this article . I think choosing the mesh setting to adjust/focus-on depends on the issue you are facing. In many cases adding a mesh constraint is a good first step for improving the mesh quality, especially if smaller feature size are limited to a smaller area while the overall simulation region is much larger. This allows for the generated mesh to have a better balance where smaller features are resolved, while reducing the consequent increase in simulation time.
Changing the volume meshing from vertex insertion to hybrid is typically helpful when the solver fails to generate a mesh (sometimes the mesh will get stuck on tesselation) for small lengthy structures (which could be part of a larger system in your simulation). In some cases the hybrid option succeeds to generate a mesh instead of the vertex insertion option
As mentioned in the documentation, deflection tolerance can be helpful for meshing curved structures by breaking up the curves into multiple linear segments. Another potential workaround for fixing meshing errors for curved structures are simplifying the geometry, for example by using polygons.