Cary L. Brown said:
Anyone have thoughts on why (other than to reuse a claustraphobic setpiece) they had these funky little crawlspaces everyplace? Has anyone ever tried to lay out the "jeffries tube" network inside of the Enterprise-D or the Voyager? I doubt that there'd really even be space for them... but it did make for some interesting technobabblish storylines!
Aside from what you've already mentioned, I'd say they were rather frequently used as an alternate route through the ship if they wanted the characters to remain unseen, or at least if the characters wanted to remain unseen, since it didn't always work.
I'd say that they may even semi-officialy be there as an alternate route. They need not go everywhere, but they do seem to connect criticle areas of the ship.