Then, I wisened up. No, this isn't the only benefit, but gosh dangit if it isn't one of the better ones. If a developer wishes, everything an application needs to run can be contained inside of itself - libraries, plugins, help files, readme files, registration information, images, and so on. Those familiar with ResEdit know what goodies they can find in an application's resource fork, but ResEdit won't be necessary when Mac OS X comes around. Gone are PICT resources in the resource fork, here to stay are packages.
Packages offer an extreme amount of flexibility.
For example, applications can include support for multiple languages. Wham, bam, merci beaucoup mademoiselle. Something for Everybody Packages are not something that will simply benefit the power users, the new users, or that weird guy that sometimes sits next to you in the office cafeteria. Packages offer a wide range of benefits to a wide range of people. Basically, packages offer the chance to get back to those old days, when relative newbies could give their friend a nifty little application and not worry about whether it had all of its libraries and extensions and so forth.