I mean, traditionally law enforcement officials require a warrant from a judge in order to tap into private communications of citizens. This means they require various things, like evidence-based suspicion, and reason to believe that such surveillance will aid in the prevention or conviction of specific crime. With this new flavour, people are surveilled en masse, without oversight, warrant, or even suspicion — just because they can be. The judicial oversight, which is lacking in the case of GCHQ, acts as a check and balance on the powers and whims of law-enforcement, and I think that's a good thing.