Speaker cable connectors? What exactly do they do?

I mean banana clips, spades etc.

From what I can discern, at the very least you get a convenience and aesthetic advantage of having caps to your speaker wire. My roommate tells me that's about all you get. He says, if you solder in the ends of your speaker cable to the connector you stop corrosion and thus loss of sound quality over time. That seems logical enough.

Do you really get a connction advantage by putting an additional mechanism between cable and amp/speaker? Can anyone explain the physical mechanism behind this and what kind of benefit you get from this?

For example:
http://www.monstercable.com/home_av/connectors/speaker_twistcrimp.asp

Maybe I just need some help. If someone could explain the basics of the importance/mechanism of this stuff, I'd appreciate it.