Brion-
With server-side collapsing, expansion will require a new request which will include re-transferring everything that's already there. That's an extra burden for the slow downloader, as well as requiring parsing and rendering time on the server.
Have you tried the feature? When you click an individual section in collapsed mode, *only that section* is loaded. Thus, no retransferring (except for the page layout). Expanding the full page should only be done when you have to edit or print it as a whole. Right now the Edit link in collapsed mode goes to the top section; I thought that was a clever feature but it's probably rather annoying. If we change this you don't even need to expand to edit in full.
Regards,
Erik