# HdSceneIndexBase::\_IsObserved() - use or avoid?

**URL:** <https://forum.aousd.org/t/hdsceneindexbase-isobserved-use-or-avoid/2181>\
**Category:** Hydra\
**Created:** [January 29, 2025, 10:37am UTC](https://forum.aousd.org/t/hdsceneindexbase-isobserved-use-or-avoid/2181 "2025-01-29T10:37:51Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![robp\_sidefx](https://sea2.discourse-cdn.com/flex016/user_avatar/forum.aousd.org/robp_sidefx/32/327_2.png) [@robp\_sidefx](https://forum.aousd.org/u/robp_sidefx)\
**Post date:** [January 29, 2025, 10:37am UTC](https://forum.aousd.org/t/hdsceneindexbase-isobserved-use-or-avoid/2181/1 "2025-01-29T10:37:51Z")

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I have a fuzzy recollection, when I started first looking at Scene Indexes, that `_IsObserved` was used extensively in the `_PrimsAdded`, `_PrimsRemoved`, `_PrimsDirtied` methods of all(?) the Scene Indexes that shipped with USD.

Looking at the code now, however, I see several/many USD Scene Indexes that don’t do this check.

What’s considered “best practice” here?