In order to simply configuration a number of transport property defaults and XmlDictionaryReaderQuotas values were changed in WCF 4.5. For exact details about changes refer this link under topics “New Transport Default Values” and “XmlDictionaryReaderQuotas”.
These new defaults will be considered only if you deploy the WCF service on a machine with .net framework 4.5. If you deploy the same service on a machine with .net 4.0, then 4.0 defaults only will be considered. In such cases, it is recommended to configure these settings explicitly.
What does that mean?
If you develop a WCF service (target framework 4.0 or 4.5) on a machine with .net framework 4.5 assuming these default values and deploy the same service: