Penis, which is relatively large in the flaccid state already and erection relatively little growing (applies to approximately 20% of all men)
The inside of the foreskin constantly emits a liquid, which medicals call Smegma. Physicians recommend to clean more frequently than only once a day underneath the foreskin with soap. The humid climate under the foreskin forms a true breeding nest for various bacteria, whose decomposition already causes a bad smell after a few hours. If circumcised it"s not only clean after bathing but all the time. Without foreskin, nothing can form or accumulate beneath it.