Hah. Wish I'd thought of some of these for last year's http://10k.aneventapart.com .

I tried to write most of my JS for 10k 'pre-minified', using tricks akin to (but not as awesome as) these. Echoing other commenters, it was largely as an intellectual exercise (to see if I could meet the 10k limit by hand) but it did make me think of a few things in a different light, and some of the 'optimizations' are things that minifiers wouldn't have done for me.

It's also a good way to get under the skin of a language, get a feel for the nuances of how the runtime behaves, and give you hints for other (more generally useful) optimisations.