Bandwidth in queue definition

I've been testing some queue setups and getting some rather strange results. 
What should be the consequences of setting a queue bandwidth lower than what's 
available? What about higher? And how should I deal with an outbound interface 
that has variable bandwidth available?

Thanks for any assistance.

-- 
Jeff Simmons                                           [email protected]
Simmons Consulting - Network Engineering, Administration, Security
"You guys, I don't hear any noise.  Are you sure you're doing it right?"
        --  My Life With The Thrill Kill Kult