Questions Regarding Deleting Source Data After Transform

From what I read from the other posts, if we are running a continuous transform, we should not delete any data from the source index as that will trigger the transform to re-compute and the deleted records will no longer be taken into account in the summarized index after refresh.

I have a few questions on that topic:

  1. Does this apply to both pivot and latest transform?
  2. If we are only interested in the summarized view and not the raw records in the source index, is there any other things we can do to reduce the storage cost from the source index if we cannot delete them? Writes into the source index can be very heavy.