I'm sure that you could try to do it without installing a module, but the question is why would you? Someone else has already figured out all of the hard stuff you'd need to figure out in order to get ssh to work from within your program - leverage their work. You'll get your job done quicker and you won't be reinventing wheels.

From the Net::SSH::Perl docs (Ben said this better than I did):

One advantage to using Net::SSH::Perl over wrapper-style implementations of ssh clients is that it saves on process overhead: you no longer need to fork and execute a separate process in order to connect to an sshd. Depending on the amount of time and memory needed to fork a process, this win can be quite substantial; particularly if you're running in a persistent Perl environment (mod_perl, for example), where forking a new process is a drain on process and memory resources.
It also simplifies the process of using password-based authentications; when writing a wrapper around ssh you probably need to use Expect to control the ssh client and give it your password. Net::SSH::Perl has built-in support for the authentication protocols, so there's no longer any hassle of communicating with any external processes.