[Carpetsmoker]

From the FreeBSD handbook, chapter 4.2:

Package Benefits

• A compressed package tarball is typically smaller than the compressed tarball containing the source code for the application.
  
• Packages do not require any additional compilation. For large applications, such as Mozilla, KDE, or GNOME this can be important, particularly if you are on a slow system.
  
• Packages do not require any understanding of the process involved in compiling software on FreeBSD.

Ports Benefits

• Packages are normally compiled with conservative options, because they have to run on the maximum number of systems. By installing from the port, you can tweak the compilation options to (for example) generate code that is specific to a Pentium 4 or Athlon processor.
  
• Some applications have compile-time options relating to what they can and cannot do. For example, Apache can be configured with a wide variety of different built-in options. By building from the port you do not have to accept the default options, and can set them yourself.
  
• In some cases, multiple packages will exist for the same application to specify certain settings. For example, Ghostscript is available as a ghostscript package and a ghostscript-nox11 package, depending on whether or not you have installed an X11 server. This sort of rough tweaking is possible with packages, but rapidly becomes impossible if an application has more than one or two different compile-time options.
  
• The licensing conditions of some software distributions forbid binary distribution. They must be distributed as source code.
  
• Some people do not trust binary distributions. At least with source code, you can (in theory) read through it and look for potential problems yourself.
  
• If you have local patches, you will need the source in order to apply them.
  
• Some people like having code around, so they can read it if they get bored, hack it, borrow from it (license permitting, of course), and so on.