bad motor mount

i have a bad motor mount on the driver's side but im hearing mixed things about what are the consequences of it. its not totally shot but it is leaking that dark gunky fluid bad and some people are telling me i dont really need to replace it and other people say do it asap because it puts stress on my cat and exhaust and after time it will like "snap it"

its puts stress on the exhaust... and doesnt always but can cause problems

so for one that people say is leaking pretty bad, how serious is it if i dont change it out

PM sineo she had some issues with the mounts.