The butter knife is a weak but somewhat common weapon in Project Zomboid. The butter knife is meant for combat-only purposes.
In the beginning, if there are zombies right in front of your spawn point, and you desperately need a weapon, and there is only a butter knife, by all means use it. It is not suitable for dealing with 3+ zombies, its range is similar to the hammer, but its damage ranks far below any other weapon (except the plank). It has no knockback capabilities (unlike the plank). If you find a better weapon, replace it. One miss with the butter knife and you are vulnerable to attack.