Keywords are added to pages to make them searchable. A page with a keyword returns all its products when searching on the keyword. The products returned are from the primary list. Keywords do not redirect to the landing page.
There are no "global" keywords, they are set individually, per locale.
Use keywords in the following cases:
To make a specific category searchable.
Example: Searching for "black friday" is to return all products on the Black Friday page.
To have a "synonym" to a category.
Example: To make "holiday" return the same products as a Christmas page. Use both "christmas" and "holiday" as keywords for that page.
To map a search phrase to a specific set of products.
Given Elevate's product understanding, it is unnecessary to add a keyword for a category like 'trousers' as Elevate can find trousers on its own.
Generally, use keywords to make a page searchable and use synonyms if there are words you want to map to something else.
See also: Synonyms