I personally use it to apply the same settings for the child dataset. For example, the parent Media dataset can have a blocksize of 1M (or even 4M) instead of the default 128K and light compression (lz4) instead of heavier zstd-3 (my default for one).
Also, you can apply the same snapshot schedule for the parent dataset. Thus, you can effectively exclude data that doesn’t need frequent (or any) snapshots.
Aiui, you can also apply different replication settings to the parent datasets.
Dan already answered this. To better understand the differences between pool geometries, you should read this guide.