There is a wax ring between your toilet and the floor --- which prevents moisture from leaking out of the toilet and onto the floor and sub-floor surrounding the toilet.

What's the worst that could happen if you don't replace the wax ring?

• moisture damaged sub-flooring?
• stains on the flooring?
• the toilet falling through the floor?
• how about mushroom growth around the base of the toilet!?
  

Yes, the photo at the top of this post is really mushrooms growing around the basement of a toilet.  And yes, those are native species -- I took this photo earlier this week in a property in Harrisonburg.