Rolling over indices using ISM and index templates

Hi,

I see that I can implement time based rolling indices in 2 ways -

  1. Configuring policies in ISM that define when an index needs to be rolled over.
  2. By creating an index template and just using the new roll over index name in writes. This auto creates the index with required configuration and adds the docs to the index. For example : if the current index is test-2020.12 and I want it to roll over to test-2021.01. Instead of creating an ISM policy, I just start inserting docs to test-2021.01. This will auto create the index using the template defined for test-*.

Is there a reason why I need to choose 1 over 2? 2 seems to be simpler and I’d would like to use 2. if it’s harmless.

Thanks,
Priya