Answer:
What is never used unless it's in a tight place?
As a whole, I am both safe and secure. Behead me, I become a place of meeting. Behead me again, I am the partner of ready. Restore me, I become the domain of beasts.
This is rectangular, hollow and has a lid, and where you’ll find it you might wonder, it is just six feet under. What is it?
No matter how little or how much you use me, you change me every month.
What an fill a room but takes up no space?
You use it between your head and your toes, the more it works the thinner it grows.