Difference between Distinct and All array indexes re: Performance

I’ve noticed countless examples on the web showing the creation of indexes on arrays. Almost all examples use the “DISTINCT ARRAY” syntax at the beginning of the definition:

          ON `travel-sample`(DISTINCT ARRAY i.flight FOR i IN schedule END, schedule)
          WHERE (type = "route") AND (array_length(schedule) < 10);

What is the behavior between ALL and DISTINCT when it comes to indexing? I have scoured the documentation, but there is no clear explanation. I have tried both ALL and DISTINCT and neither seem to affect results or query time.

In CREATE INDEX statement
DISTINCT ARRAY … is used the index will have distinct values for the each document. any duplicates in the given document will be index only once.
ALL ARRAY … is used all the values in the each document will be indexed.

DISTINCT makes array index size small if there are lot of duplicates and can use less resources.
Some cases of of UNNEST queries can take advantage of ALL index and do covered scan (Check Summary)