Why a 1/4" gap at the bottom of the hatch?

Folks,
I realize there is a need for a 1/4 inch gap at the top of the hatch for the hinge to be able to swing without binding.
What is the purpose of the gap at the bottom that some people put in?
I'ms not clear about that.
Thanks,
Jim
I realize there is a need for a 1/4 inch gap at the top of the hatch for the hinge to be able to swing without binding.
What is the purpose of the gap at the bottom that some people put in?
I'ms not clear about that.
Thanks,
Jim