This is something that has been a "design" since version 1.3 (iirc), and shouldn't be.
If you have the debug options set to '1' or higher, it showed the page generation time, number of queries, server load, and if gzip is on.
However, the server load will always be '--' unless you have set a server load limit.
Personally, I think this should be changed, so that it always displays the server load, providing the debug setting is there.
(I posted this as a bug, but it was closed, and I was told to post here instead)
So what do you think?