The answer is Kleenex. Now try to tell someone in a general conversation that you when you're talking about Kleenex, you meant 1) the actual company Kleenex, not the 2) product nor the 3) other generic tissue paper products. Because now you have to explain to consumers why your Kleenex is better than your competitors Kleenex, when before you could just say 'Kleenex, the brand that works' or 'Kleenex, the brand you trust' or just plain 'Kleenex'. Even if it's just a name, if you reduce the number of ways for you to differentiate your product from others, it just makes it harder to do so.