It seems likely (functionally) unnecessary in this specific case. But some prefer not to analyze each specific case to try to convince themselves that it is actually foolproofly unnecessary and so just include BEGIN for such initializations as a "best practice". (The END block is likely just a visual reminder for "this is where you put clean-up code" and "I didn't forget the clean-up code, we just don't need any for this module at this time" -- as such, I might comment it out for the sake of clarity.)

The flow of the above code w/o the BEGIN goes like:

Compile: package iControlTypeCast;
Compile: require SOAP::Lite;                # nothing happens
Compile: my $urnMap;                        # declares the variable
Compile: $urnMap = ...;                     # nothing happens
Compile: sub SOAP::Deserializer::typecast   # makes it possible to cal
+l this
Run:     require SOAP::Lite;                # compiles and then runs S
+OAP/Lite.pm
# During the loading of SOAP::Lite, a whole ton
# of stuff can happen and is likely to happen
Run:     my $urnMap = ...;                  # the variable is /finally
+/ initialized
[download]

In this particular case, it seems unlikely that anything that happens during the loading of SOAP::Lite would lead to SOAP::Deserializer::typecast() being called. But I'd actually have to study the SOAP modules quite a bit more before I was fully convinced of that. It would certainly be bad style for that order of execution, IMHO. But I see no reason to just rely on such an order of execution never arising.

So it seems wise to avoid the window of time where SOAP::Deserializer::typecast() can be called while $urnMap is still not initialized. The BEGIN block avoids exactly that. So, I consider it good style/practice.