The determinism slider tells the SoC how to operate; by default, it is set to performance determinism.
"Performance determinism" tells the processor to run in a consistent manner which allows consistent repeatability when doing benchmarks or performance testing. The processor will run at the best performance with little deviation allowing repeatable runs.
"Power determinism" allows each individual processor to run at the maximum allowable performance on a per die basis. This means that process deviation will not be accounted for and if benchmarks or performance runs are made, there will potentially be differences between runs and between processors. The amount of deviation is dependent upon process as well as other system characteristics such as thermals.
Determinism can be used as needed, but for the most consistent operation, the "performance determinism" mode is recommended.