Another one I used to use was Treesize Pro.

It's not so common now but people always used to say "I've run out of space so I deleted some documents and stuff but it only gave me 20Mb more". Inevitably you'd find a 900Mb temp file using up all their space and they deleted a load of stuff for nothing.

The simplest method is to just search for all files over (say) 50 Mb and sort the list in descending order.

Gareth