The mitigations applied to exorcise Spectre, the family of data-leaking processor vulnerabilities, from computers hinders performance enough that disabling protection for the sake of speed may be preferable for some.
Disclosed in 2018 and affecting designs by Intel, Arm, AMD and others to varying degrees, these speculative execution flaws encompass multiple variants. They can be potentially exploited by malware via various techniques to extract sensitive information, such as cryptographic keys and authentication tokens, from operating system and application memory that should be off limits.
Though a lot of research has gone into the Spectre flaws, and work done to prevent their exploitation, basically no miscreants are abusing the weaknesses in the real world to steal information, to the best of our knowledge. There in lies the rub; does one keep the protections on and take whatever performance hit arises (it does depend enormously on the type of workload running) or switch them off because the risk is low? Or, from another point of view, put speed promised by chip manufacturers over security that was supposed to be present.