I have recently bought my external components and a Celeron 2.6GHz S478 for a PC to sell. What I do is that one is an External HDD and the other one is an external DVD Burner. The HDD I use for backups. I backup impotant files such as Music, Wallpapers and documents required. And, I check that everything is done. THEN I reformat and I realise I forgot a stupid file that I downloaded for free
The External Burner is great for other PCs without DVD burners or any optical dirve for burning their data or even using Norton Ghost.