Do we need to include a spatial structure in every IFC-file we export?

[JanErikHoel]

Problem
I was encouraged to repeat a question I had on the Slack channel for Implementers Forum in this "channel" as well to reach a wider audience.

The question was:
A question I got from one of our Product Owners in US:
Do we need to include a spatial structure in every IFC-file we export - or is it enough to export physical entities e.g.?
Must ifcSite always be included e.g.?

Answers I got
Léon van Berlo:
The requirement for ifcproject, ifcsite, ifcbuilding is coming from the reference and coordination view
(https://bsi-technicalservices.slack.com/archives/C042ZUVGBTP/p1687334690174229)
so it is required if you support the use cases of reference data and coordination; it is not a requirement for other use-cases
(https://bsi-technicalservices.slack.com/archives/C042ZUVGBTP/p1687334745532389)
since there are little vendors that support import other then these use-cases it will require some agreements to make sure import of some other spatial structure is supported
(https://bsi-technicalservices.slack.com/archives/C042ZUVGBTP/p1687334783171769)
in other words: we cannot be sure if another spatial structure can be imported by any tool

Evandro Alfieri:
As a corollary of last week discussion on "link between alignments and project", the only entity that is mandatory for the exchange is IfcProject (because all alignments must be related to it, directly or indirectly). But the presence of IfcProject is already covered by a WHERE RULE.
Coming to IfcSite, both domain experts and vendors pointed out that there might be cases with 1 or multiple sites (or even 0, e.g. when only alignment data is needed in the exchange). So, at the moment, there is no documentation nor agreement for IFC 4.3 that forces you to include an IfcSite in the exchange. Let alone any other spatial structure elements. Situation might change in the future, but this is the current status.

Summary
So for me it seems that none or whatever spatial structure can be included in the IFC-file we export out from our BIM-model.