Available settings to increase performance

Note: All forms of performance increase come with a slight decrease in overall image render quality.

Noise threshold
Set this value higher up to 1.0 to increase renderspeed, at the cost of more grain in your final images. Set this value lower, up to 0 to improve the render quality, at the cost of speed.

Light Paths
Max bounces should reflect your project. Use a sensible amount of bounces per category, depending on your scene. Example: scenes with loads of transparent assets such as e.g. foliage should have a high enough amount of transparent bounces. A scene with loads of reflective objects should have enough Glossy bounces. The total bounces should be equal to the highest number within any of the categories. E.g. if transparent is set to 8, the total should also be set to 8.

Reflective and refractive caustics can be enabled if you're working with glass-like objects. Enabling these, or increasing the amount of bounces, comes with a loss in renderspeed.

Fast GI Approximation, makes estimates based on lighting in the scene to 'fake' Global Illumination. This results in darker and less realistic, but faster, renders. Disable this if you're going for realism.

Performance
Within the performance tab only Persistent Data has been enabled. This will speed up renders by temporarily storing data within your scene for faster usage when rendering. This can give artefacting when using moving objects in your scenes. So for complex animations it is advised to turn this OFF.