Here is how a standard "Full Set" looks vs. a 1G1R set:

The benefits of utilizing a 1G1R repack are numerous. The most immediate advantage is the drastic reduction in storage space. By eliminating duplicate regions, beta versions, and broken dumps, a ROM set can often be reduced to a fraction of its original size without losing a single unique playable title. This space-saving is particularly crucial for users running emulation setups on devices with limited storage, such as single-board computers like the Raspberry Pi, handheld emulation consoles, or modded classic consoles.

If you want to build your own 1G1R set rather than downloading a pre-made one, these tools are the community standards: Make a 1G1R ROM set - One Game, One ROM

For European releases, filters can prioritize English over French, German, or Spanish versions.

For 1G1R generation, a typical Igir command looks like this:

Cleans up your emulation frontend by removing clones, hacks, and broken betas.