There are few ways to look at this question - Whereas, in it's most basic form, asking where to use LWP::UserAgent in place to SOAP::Lite, is right and appropriate, this query in truth probably raises more questions than it answers. The reason is because, where as LWP::UserAgent provides an appropriate transport conduit for a pre-fashioned XML request, it is not immediately comparable to SOAP::Lite as the latter not only provides transport for a variety of access modalities (such as HTTP, TCP and FTP), but also methods for abstraction for the submitted request, response received and contained data structures. As such, in turn, the question should instead be fashioned around the context of where this code implementation is to be employed - Is there likely to be later changes in transport or data structure? Is there likely to be any variance in structure or form of the responses which are likely to be received? How complex are the responses from the SOAP service likely to be? Is there a requirement for abstraction of the lower-level transport for employ within higher-level applications or APIs?
These questions are likely to provide a better construct within which to answer your questions than those which you have posed in your post.
perl -le "print unpack'N', pack'B32', '00000000000000000000001000000000'"