It depends on whether your penis is overtrimmed or not.
If your penis is overtrimmed, your hard erection will force the penile cylinders to expand into your perineum, resulting in a high pressure against your perineum and prostate. You will feel very uncomfortable, even pain, down there, upon a hard erection. This can cause premature ejaculation.
If you have sufficient foreskin, a hard erection will expand the penile cylinder toward the free end, the glans penis. This is what the Penile Ballooning Method is all about. Please use the following graph as your reference for this discussion.