I'm glad I could help you
Well, the normal "system save and load" uses json too, but it stores data in either WebStorage or IndexedDB
(I'm not really sure where it is exactly), which are in theory "permanent storages" and are not affected by the user clearing their cache.
However if he uses a program such as CCleaner, the savegame may be erased... (that's what appened to me ^^')
So to avoid problems and prevent the user to lose his savegame, it's important to save the game in a file, especially if your game is a desktop application.