Audio Systems: Firewall, sony cdx, pioneer radio

Question
I have purchased Sony CDX-GT250S CD player with Sony compatible speakers, I am not using additional amplifier. On the back of the CD player there is a rubber bush that has a through hole and a pin passes through that hole and has threads at the other end which tight in the back of the CD player. I have seen the instructions manual and this bush has been named as firewall.

In fact the CD player cannot be installed with the firewall attached with it because there is no enough space at the back of the CD player so I have removed the firewall.
Now I have installed the CD player and it is working fine. My question is that what is the purpose of firewall? Should it be always attached to the CD player or is it useless with my setup and I have done the right thing?
Thanks
Kalson  

Answer
I did use that and install it in my vevhicle, but i didn't use it and remove the screw and plastic on my wife pioneer radio  
i did the same on the other 500 radios i install i have the little ruber and screws  all over the garage never use them
you are ok