For Speedrunners: Save files are essential for practice mode.
For Trophy Hunters: Be aware that Sony’s Terms of Service technically prohibit using "third-party save data," but enforcement is nearly impossible. As long as you do not use the save to unlock obvious cheats in online leaderboards (there are no online leaderboards in Thieves in Time), you are safe.
For Gamers: The game is about fun. If the bottle hunting or tedious hacking mini-games are ruining your experience, a 100% save file can rescue the joy of playing as Sly Cooper.