There is perhaps a difference between a) writing a song to given words as in a student's songwriting exercise, and b) having a friend who is a good lyricist give you words for which he/she wishes a tune: I have done the latter on several occasions. We are not able to sit down together to work the tune out, and to a certain extent he gives me free rein, tho' I would usually read through the words and then ask him what was HIS concept of what style of song it was to be, before taking it away to work on it.
On the whole, he has been happy with what I have come up with, even to the extent of occasionally allowing my comments or suggestions for fitting the words to the tune via some minor amendments.
On one occasion only he really did not think the tune I had written was anything like what he had in mind for this song: but no tune is wasted - I just kept it and used it for something else, one of my own songs!