What are the benefits of nitrogen-filled tyres?

I recently had two new front tyres fitted on my 2004 Peugeot 307 SW and the tyre depot decided to fill all four tyres with nitrogen without asking me first. Aside from that I would like your opinion on the pros and cons of having nitrogen-filled tyres instead of air, as I haven't heard of this before.

Asked on 16 June 2012 by MT, via email

Answered by Honest John
No cons. Air is 80 per cent nitrogen anyway. Filling with pure nitrogen means less variation in pressure from changes of temperature.
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