For most of people bitcoin being anonymous is an advantage. But for police this is a big disadvantage ,maybe the biggest one. People can buy drugs, fake identities, prostitutes and all kinds of illegal things with bitcoin. Yes, you can buy that with real money but that would be a lot easier to discover.
The big fees for low transactions(lower than 20$) are also a disadvantage. Bitcoin cannot be used to buy things like a coffe or a sandwich because you would pay double or triple of the normal price.