It all depends. People tend to take Bitcoin's 'anonymous' nature a bit too serious. Nowadays, most exchanges require their users to fully verify themselves in order to keep using that exchange, where some exchanges even tend to freeze all your funds till you have done so. Every coin you withdraw from such exchange will have your information tied to it, and from there the exchange can basically follow everything you do. It might not sound like it is a big problem at first glance, but it will be when governments force exchanges to hand them over all user details. Everything at that point can, and will be used against you. Especially if becomes clear that you haven't been paying any tax, that you have spent your coins on illegal goods, etc. That's why I always advice people that if they happen to withdraw coins from an exchange, to run them through a mixer. It of course won't guarantee you 100% privacy, but it greatly contributes towards something close to that.