Many biologists are familiar with the phylogenetic inference software PAUP* in the Macintosh 'Classic' GUI (Graphical User Interface) environment. However, running PAUP* in GUI mode on a personal Mac computer is not incredibly efficient, as any other running applications dramatically slow down its progress.
Learning and using the UNIX command line with a server-based PAUP* application can take the load off your personal computer, to free it up for more important things, like that latest manuscript you're trying to write. Furthermore, other phylogenetic inference software, such as MrBayes, only run through a command line interface. Moreover, the UNIX server environment is inherently more stable than your desktop environment - this helps keep your multiple day analyses running for as long as it takes. Getting access to these resources requires network access to UNIX server computers, and the ability to comfortably operate in the UNIX command line environment.