This is mostly a complete copy from microsoft.com
When users access a resource using Windows authentication and authorization (for example logging on to a workstation or accessing a file share), an “access token” is built to represent that user.
The number of SIDs (representing group membership, etc) in that token largely determines how much kernel memory space (Paged Pool) is required to store each copy of the token.
These allocations follow a “stair-step” pattern, as follows:
At approximately 84 SIDs, allocation jumps from 4KB to 8KB.
At approximately 177 SIDs, allocation jumps from 8KB to 12KB.
At approximately 270 SIDs, allocation jumps from 12KB to 16KB.
At approximately 363 SIDs, allocation jumps from 16KB to 20KB and so on.