Because it's nice to get rid of all the rubbish under the bonnet and makes it all look a bit tidier.
On my 90 I have not bothered to take it off yet, I have the plate and I even have an old 300tdi EGR junction pipe which I cut the exhaust insertion pipe off and welded it up, cleaned it up, painted it, looks like the real thing! So I really ought get round to doing it.
Did it on the Disco though.