IBM provides a good introductory document on different WSDL Binding Styles. The most common are RPC/encoded and Document/literal. WS-I Basic Profile also recommends Document/literal, which seems to become the broadly accepted standard. This encoding style should actually be sufficient in most of the cases, plus it provides the possibility of validating SOAP messages against their XSD schemas.
Well, there are always people who know better, e.g. certain government agencies that provide webservices, and somehow decided they had to use the completely uncommon RPC/literal binding style. This means that
(a) .NET 1.0 / 1.1 clients cannot access their webservice, as the .NET framework webservice implementation does not support RPC/literal. Admitted, there is a workaround, but that's definitely not something for the average programmer who drags and drops the webservice's reference into Visual Studio.
(b) SOAP messages are cluttered with unnecessary type encoding information on each request/response.
Of course those are the same folks that publish hand-coded (hence errorneous) WSDL-files.
