So I downloaded a game and then eventually deleted it, but a while later I ended up installing it again and realized my save data was still there. I tried this with other games I installed and the same thing. I want to delete this save data if possible since I don't know if it's taking up space, or if it's some other stuff that just doesn't sit right with me. At the very least I would like to know if I can even find those files at all, or if it's just a background thing that really does nothing.

Sorry if this is a dumb question but I feel like I have to know. 

That depends on the game. You have to figure out where they store data. That's usually in the %APPDATA% directory on Windows, and under .local/share/ in Linux (both in your home directory). Hope this helps.