Other than the religious aspect of circumcision, there was thought at one time that the circumcised penis was 'healthier'; that is, easier to keep clean, etc. It is easier to keep clean, but any guy who cares about his cleanliness will draw back the foreskin when he showers or bathes and wash himself. Conventional wisdom is not always wise.

One aspect of the difference that people have not addressed is the ability of a person with an uncircumcised penis to last longer during coitus--that is, to ejaculate less quickly. That is due to the foreskin covering the glans penis (the cap or head) and thus preventing the degree of friction that a circumcised penis would experience. However, other literature demonstrates that that can be overcome (hehehe) by mental control and the importance of the female's experience to the male involved. IMO, of course.