When dick size is the most important thing ever...
Remember that scene in Total Recall when Arnold Schwarzenegger has to trigger the alien atmosphere'omatic? If only a certain size dick could save all of life on Mars, then peen size matters.
Remember in Temple of Doom when Billie had to put her hand in the creepy crawling hole of doom to save Indie and Shortround from impalement and imminent squishing? It would be bad if a peen came up an inch short.
Other times..
Nude Carpentry

Human Sundial
Peen Ring Toss - though a shorter peen would add difficulty for advance levels