This fashion issue depends on the material or fabric of the trousers. If it’s a dressier fabric, such as tropical wool, then it should have a crease. If it’s a more casual style, like chinos, then no crease.
All my dress trousers have a crease down the front, but my city shorts and casual, cotton pants, do not. My trousers jeans do have a crease since they are a dressier denim and styled like a dress pair of black pants. However, this is a personal preference as I like the slimming effect it has on the line of leg. In general, a crease is usually makes the trousers more formal.
