I made one for my son a few summers ago when he went off to be a camp counselor. He said he liked that it was personal, had my writing on it, and it was nice to have both the one that matched his sheets and the one I made because he sometimes wanted or needed to change just the pillowcase mid-week, not the whole set.
I change pillowcases mid-week or more often myself. I'd appreciate a personalized one. Monograms are always special for married couples. I just finished making a set of 20x20 (each of their first initials) and a 14x14 (their last initial) for newlyweds in the family. They love them.
I wouldn't make pillowcases just to use up scraps or if I knew they don't appreciate handmade gifts. You have to know your recipient.