Question about whether or not to create an Encoded Vector Index (EVI)

I have just started reading about Encoded Vector Index (or EVI)
One of the points that seems to be stressed is cardinality as far as the key is concerned.
The states of the USA is good cardinality as there are only 50 of them.
Timestamps are bad, because you can have up to a kajillion of them.
How do you determine what is good and what is bad?
For instance, a date field (or at least a numeric field which represents a date), would that be considered a bad choice for cardinality.
Cardinality - I hope I have the correct word


Alan Shore
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