If the value of HttpGetUrl is relative, the address at which the metadata is published is the base address and the service address plus a ?wsdl querystring.
If the value of HttpGetUrl is absolute the address at which the metadata is published is the value of HttpGetUrl value plus a ?wsdl querystring.
For example, if the service address is http://localhost:8080/CalculatorService and the HttpGetUrl is an empty string, the HTTP/GET metadata address is http://localhost:8080/CalculatorService?wsdl.
If you do not enable this property and do not change HttpGetUrl or set it to a relative address, an exception is thrown at runtime when the service host is opened without a base address for HTTP.