Well I'm here to tell you that this is a treasure trove of data that is often targeted by malware, in order to use the data for mischievous things like abusing them, or selling them off to someone who will.
The malware attack aside, there is a possibility for close relatives and friends to even steal your important information from you just by making use of your browser.
I can remember sometimes that last year I made a registration to some freelancing site using my coursemate device, and I remember using the save password option on Chrome.
When I was finding it difficult to recall the pass just because I knew the guy's phone password, I was able to access the inbuilt Chrome password saver, and my details were not the only thing visible there. Someone with ill intentions can easily sneak on any information needed from their work, just the phone password. You can grab all the saved data in his browser.