You generally do not have to create these yourself, but understanding the tools helps you appreciate the process. Most repacks are generated using software that filters XML dat files.
The "Repack" Process:
The acronym 1G1R stands for One Game, One Revision. 1g1r rom sets repack
The philosophy is simple: Instead of storing every single dump of a cartridge ever made, a 1G1R set keeps only the definitive, playable version of each unique title.
Here is how a standard "Full Set" looks vs. a 1G1R set: You generally do not have to create these
Full Set (Example for Super Mario World):
1G1R Set (Same game):
The Rules of 1G1R:
If you are going to download a repack, prioritize these systems where bloat is worst: The "Repack" Process: