Compared with "must haves," "nice to have" suggests a more inclusive approach.
It may indicate a culture that values employees and realistic goals -- all good things.
However, wishy-washy "requirements" attract bozos that you'll probably end up having to compensate for down the line. "Nice to have" may also mask a recruiter's indecisiveness too, so be cautious.
Remember, your preferences matter too. Just be sure to express them as "must haves!"