In some Hadoop related processors (e.g. GetHDFS, DeleteHDFS) the "Hadoop Configuration Files" property supports expression language. This is convenient, as the lengthy paths to the config files can be stored in a property file loaded by Nifi at startup or in an environment variable, and the name of the property/environment variable can be referenced in the processors' configuration.
The controller service HBase_1_1_2_ClientService also has the "Hadoop Configuration Files" property, but it does not support expression language. For the convenience reasons described above and for uniformity, it is desirable to allow expression language in that property as well.