AEP guardrails 'Data model limits '

Are there better/simplified explanation for these guard rails ? https://experienceleague.adobe.com/en/docs/experience-platform/profile/guardrails

1) A maximum of 5 multi-entity relationships defined between primary entities and dimension entities is recommended. Additional relationship mappings should not be made until an existing relationship is removed or disabled.

2) The optimal array cardinality in a profile fragment (time-independent data) is <=500.

3) The optimal array cardinality in an ExperienceEvent (time series data) is <=10.

4) The maximum number of identities in an Identity Graph for an individual profile is 50. Any profiles with more than 50 identities are excluded from segmentation, exports, and lookups. We have learned that AEP have mechanism of auto deleting the Identities based on priority once the 50 count is exceeded. Does it mean even though the Identities never exceed 50, as they keep on deleting, it would still be execluded from segmentation, exports, lookup ?

5) Time-series data is not permitted for non-XDM Individual Profile entities in Profile Service. If a time-series dataset is associated with a non-XDM Individual Profile ID, the dataset should not be enabled for Profile. What does it mean ?

6) You should not create a relationship between two non-XDM Individual Profile schemas. Schemas are always XDM, so what does non-xdm schema mean ?

7) The ability to create relationships is not recommended for any schemas which are not part of the Profile union schema. Does it mean we should not create lookup relationship with profile/event schema if both profile/event & lookup are not enabled for profile ? What happens if we try to do it ?