What is this part and where does it go?

I followed the excellent guide to replace the dock connector in my iPhone 4.

It now works! which is great and all phone fucntions seem fine.

During disassembly this part fell off another one and I can't see from the instructions where it is supposed to go...

Phone is reassembled currently and working fine however Apple aren't known for making extraneous parts for their products so I think its probably useful for something ;)

I think that its supposed to secure the rear camera maybe?

Thanks

Edit: sorry didnt realise the pic wasnt attached...