The biggest advantage of perl is probably its huge library of modules. In the past, most of us started learning perl because we needed access to DBI for database access, CGI for web applications or TK to develop GUI applications. We adopted it as our primary language because it supports applications from simple one-liners to large OO projects.

Although I would no longer recommend CGI or TK for new applications (newer modules are preferred), perl modules are available for almost any application area.