[G4] Mac Classic Environment

[Karl Armstrong]

I believe Classic is still part of the default install for OS X. I would strongly suggest that you do not mess with the defaults unless you understand what you are doing. In this case, leaving Classic installed will harm nothing, and will possibly be useful.

Long version:
Prior to the introduction of Mac OS X, Mac computers used a radically different operating system. Applications written for Mac OS 9 and earlier may not run directly under OS X. Apple shipped a tool in the original and subsequent versions of OS X that emulates a 'Classic' Mac running OS 9 in a virtual machine to support these legacy applications.  It's a tiny bit slower at some things, and takes forever to launch, but it usually works.
Even before OS X officially shipped, Apple also shipped a bridge application framework that allowed developers to write application for both operating systems, known as Carbon. Most of the major applications shipped in the early years of OS X targeted this framework, so there are a lot of applications that will run on either OS. It's mostly stuff from the early System 8 days or earlier that will only run under classic. You are not likely to run in to much new software that even can run on the older system, and probably none that require it.