In clan matches, voice chat can mean a big difference between winning and losing. RW is used by alot of clans, as well as Team Sound, and BattleCom. RW is quite basic and works well. Sound quality is a bit low, but understandable. Team Sound and Battlecom have better sound quality. They also have features to bind "words or custom speeches" to keys. However, ever member must have the speech pack loaded or they won't here the speech. They also have the ability to seperate members into Attack or Defense, or more exactly team A and team B. This is great for clan practices where one host server can host both sides. RW doesn't support this feature and requires two seperate host servers. TS and BC take a bit more bandwidth than RW.
As for these proggies taking up alot of bandwidth...it's not that bad where it causes packetloss. It depends on who is hosting and how good your modem is online really.
Comm is very important in games, and with voice comms, it greatly enhances the ability to defend and attack.