The foreskin can be so tight that you can not pull it back. At birth this is entirely normal.
Most guys can pull it back when they start their teens. Some only succeed doing this when they are 15 or 16 years old.
When your foreskin is tight masturbation and intercourse can be painful.
Smegma can accumulate between glans and foreskin since you cannot retract the foreskin to clean underneath. This makes the glans prone to infections.
You run the risk of paraphimosis.
Be aware that a tight foreskin is sometime misdiagnosed as phimosis. The doctor may then recommend circumcision, while you could possibly solve the problem by stretching your foreskin.

How to stretch a tight foreskin?