The aforementioned instructions will definitely reclaim hard drive space. Your Classic folder (i.e. the System Folder) takes up physical (well, sort of physical) space on your drive as does any collection of files and removing it will give you back hard disk space. It may speed up your computer a little if you don't have to boot into Classic (definite speed boost) or run Classic support pieces of your system (minor speed boost).
Also, be sure to toss the Desktop Folder at the root of your hard drive, and if you feel you can search your drive and remove any applications that don't open without booting Classic (mostly in the Applications (Mac OS 9) folder, I bet).