I've recently installed the Tomato firmware (v18) on my Buffalo
router, and am very impressed. I now would like to experiment with the
QoS capabilities, but am a little confused.

On the QoS Basic Settings page, there are places to enter Max
Bandwidth for outgoing and incoming data. Is this the TOTAL maximum
bandwidth for ALL traffic? If it is, I presume the purpose is that
when the various classifications are assigned a percentage, it means
they will use at most that percentage of the declared overall maximum.
But isn't that likely to waste some of the potential bandwidth? Or do
the QoS rules only fire when there is no spare bandwidth available?

For example: Suppose I limit BitTorrent to 25%. If the WAN is
completely idle, will BitTorrent then be allowed to use 100% until
some other application comes along and wants some bandwidth?

Is there an in-depth discussion of how QoS works anywhere?