smartpool file pool policy

Hello Good day to you all.

I had a query on smartpool file pool policy.

1/ when we define policy based on modified / access I understand the option "is older than" to find older files, but I couldn't understand the option "is newer than".

Assume I'm creating a Tier policy to move 6 months old data to archive nood-pool for which I can use
" is older than" option. when do we use "is newer than" option can you please help me understand on this option with an example.

Also when we use "access" option why is that we need to enable "This criterion requires that Access time tracking is enabled" which they say is a overhead on the cluster.   thank you