Preloading files - all that useful?

I was curious, what extly would be gained by using the trigegr Preload files?

I was thinking, if maby I could have it preload a JASS file with functions in it, that'd be great. But will it work?

Basiccly I'm asking can Preloading actually be used for anything really useful (not in a campaign, multiplayer)?

And for preloading mdxs, does it actually make the game any faster?