The optimization of Memory Cleaner tries to restore the system’s memory state to the state of a “fresh system restart”, mostly by forcing the system to empty caches and lower compressed memory. This only speeds up your system in special scenarios:

  1. After closing a memory intense app, it will clean up the caches left behind. In case if you know you will not start a memory intense app again in the future an optimization helps your system.
  2. Before planing to run memory intense apps.

Auto optimization does not have a fixed threshold, it runs the optimization when monitored memory values indicate that optimization will be effective (i.e. after you close a memory intensive app and in several other scenarios)