Bandwidth charges would come into effect if you opt to use the TURN server and / or the MCU server. These would be optional for you, and you would switch them on depending on your use case. We have customers who have minimal need for those servers, and others who need them more frequently.
TURN is necessary when one of the peers is behind a symmetric NAT and the other peer is behind either a symmetric NAT or port-restricted NAT.
MCU comes into play where you have large multiparty conferences, where where having every peer connect with every peer on the call overloads the client device and bandwidth. Other operations such as transcoding and recording also are done through the MCU.