There are several reasons why you would want to be able to find your save files if you are a Oxygen Not Included payer. Among the popular reasons, one is to generate backups that prevent progress loss in case saves are lost or corrupted.
These backups are doubled as saves; you can get back to it at a later date for mere nostalgia or to check how much of progress you have made in the game. Certain third-party applications that let you change your game saves also need access to the save files. That is why it is important to know where your saved files are.
But the question should not be why you would want to access your game saves. Rather, it should be how you can access them. For your operating system, you can get help below:
Windows editions of Oxygen Not Included store game save files at:
To open that path, just paste it into the address bar at the top of a File Explorer window and hit ENTER.
On Mac, you can find your Oxygen Not Included save files in this folder:
~/Library/Application Support/unity.Klei.Oxygen Not Included/save_files
Open up Finder, press COMMAND + SHIFT + G, paste ~/Library/Application Support/unity.Klei.Oxygen Not Included/save_files into the text box and click Go to go to that folder.
Linux editions of Oxygen Not Included store save files at this path:
~/.config/unity3d/Klei/Oxygen Not Included/save_files