Now that you have a special, date marked folder containing just your source code and nothing else, you could simply copy it to a DVD. Actually, there is absolutely nothing wrong with doing that.
However, compressing the folder has two advantages: * the data is smaller * you only have a single ZIP file to deal with
If you want to upload your backups offsite, these could be significant benefits.
7-Zip File Manager is a well known, open source, ZIP compression utility. You can run it from the command line (eg from a batch file) so it can be automatically incorporated into your backup script.