The skin on the penile shaft is thinner and looser than on the pubic mound. This requires a change in visual focus and tension.
Before trimming, look down or use the mirror. You’ll see: Trimming pubes and testicles a visual guide
About 30% of men have hair that extends onto the shaft base. This hair can cause irritation during sex if trimmed too short. The skin on the penile shaft is thinner