I don't get it, how does sporadically deleting cookies help? Sites don't, I assume, store significant amounts of data in them that would get irrecoverably lost. And even for cookies identifying you it should not be too hard to stitch two histories connected to two different cookies back together on the server based on your IP or browser fingerprint. And if they were actually worried about negatively impacting the user experience, why would you not selectively destroy the cookies? Just keep my preferences and give me a new authentication token so that I remain logged in and don't loose my preferences, the browser already has a feature to delete everything. So what am I missing, how is this a useful privacy feature?