I don't think you mean 'interpolation'

People use the #!/usr/bin/env perl so that they can run the program on a variety of systems where they can rely on the presence of 'env' but don't necessarily know where the perl interpreter is located. env is a utility to run a program in a controlled environment, but in this case it is used simply for it's feature that it will find the program in the $PATH. There is no other particular advantage to use it and env is not necessarily available on all Unix-like systems.

/J\