I would recommend you right click those settings and choose "reset to default value".
The path depth controls how often a ray can bounce from surfaces.
The further a ray bounces, the lower its contribution to the look of the scene becomes.
High path depths can introduce noise and use up GPU RAM.
Try to use the lowest path depth possible without screwing up reflections or refractions.
For the kind of scene you showed in the first post, considering you are rendering on GPU, I would recommend this:
- Engine: Path OpenCL
- Total path depth 10 (because of the glass and reflective materials, you might need a bit more like 16, but only if reflections/refractions show up black)
- Diffuse depth 4, Glossy depth 4, Specular depth 10 (same reason as for total depth)
- Sampler: Sobol
- Adaptive Strength: 0.3 (set it lower if you have noise remaining in shadows)
- Filter: None (a bit better performance on GPUs)