About not recommended to use localStorage

A question about using localStorage in CanvasApp, docs describes that localStorage is denied , but I tested a website with localStorage based token storage works well.
So I want to understand the purpose (or concerns) of the prohibition of the [document statement here](https://developer.salesforce.com/docs/atlas.en-us.platform_connect.meta/platform_connect/canvas_app_iframe_considerations.htm?q=local%20storage)