a) know how to retrieve that link (i.e. what resource do I need to retrieve in order to get that response)
b) requirement for that link to exist (they still need that link).
Requiring that a client know that to get data Bar, they need to retrieve resource A, follow the link at foo[n]._link to retrieve resource B, and then following the link at _link.bar feels like a total non starter, and actually increases coupling.
