Facebook's HipHop - What's it for?

Question

The news in the PHP world today is Facebook\'s HipHop, which:

HipHop for PHP isn\'t technically a compiler itself. Rather it is a source code transformer.

Answer 1

Running machine code over interpreted code is faster. This is useful in one sense, but also reduces the amount of machines you require, as each processor has less work to do.

This is good for a company like Facebook, in that they can cut the amount of machines they need.
In terms of why it's useful for them, they probably run a lot of sorting and indexing, on the large amounts of data they have.