SQLBench never attempts to access data residing within your databases.
However, we still recommend implementing our minimum permission configuration, under which SQLBench does not have access permissions to either query or update your data in any way.
Even in the unlikely event that SQLBench were ever compromised by a malicious actor, SQLBench's minimum permission configuration would restrict the security context available to such an actor to that granted to SQLBench, which only allows collection of telemetry.