Video game emulation is useful because it allows for people to play video games they may not be able to play otherwise. Without emulation, there would be no way to play those retro games, or games that are no longer being produced. For example, MobyGames is a database of video games and computer games that stores around 60000 games, 23000 of which were computer games originally released on floppy disks or cassette tapes.1 If not for this database, those games would not be playable as they would likely be lost.
Emulation allows for access to retro video games that would otherwise be hard or impossible to get otherwise. For example, if you wanted to play Pokemon Emerald for the Game Boy Advance legally, you would first have to find a used copy of Pokemon Emerald, which goes for more than $200 on eBay.2 And if you don’t have a Game Boy Advance or DS that can play GBA games, you would have to buy one of those. That would be an extra ~$100, so playing Pokemon Emerald costs about $300.3 But with video game emulation, you can find a ROM of Pokemon Emerald and a Game Boy Advance emulator and play it for free.