Does applying slice security have any performance impact? Or is it more just maintenance impact?

I worked in an app where we had ~ 400 slices defined on a cube and we did not see performance issues. But every app is different, and I do believe the more slice you have and the more evaluations you ask OneStream to do, the potential is there for it to impact performance.

Our slices were constructed such that we started by removing all access first here in the first slice on the cube:

behaviorInGroupInFilter="IncreaseAccessAndContinue" accessLevelInGroupInFilter="ReadOnly" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="ApplyAccessAndContinue" accessLevelNotInGroupInFilter="NoAccess"

Then we added it back via a person's security group here:

behaviorInGroupInFilter="IncreaseAccessAndContinue" accessLevelInGroupInFilter="AllAccess" behaviorInGroupNotInFilter="SkipItemAndContinue" accessLevelInGroupNotInFilter="NoAccess" behaviorNotInGroupInFilter="SkipItemAndContinue" accessLevelNotInGroupInFilter="NoAccess"

And we did not have any "Stop" slices.  All of ours were "AndContinue" and even with 400 slices, performance was okay on that cube.

But again, every app and data model is different so the potential is there.