Sure - as mentioned in my previous comment it gives you an entire history of communication to retroactively analyze.

It's not likely to reveal much alone (too much noise - like you suggested), but given a lead from some other means you can use it as a tool to look through the recent communications of that suspect and their close network.

This would be a tool that would be useful to have and since people planning violence are likely communicating about plans - looking at comms could lead to actionable intelligence.

Is this potential intel worth the risk of abuse? I think probably not, but that should probably be decided by the society being surveilled. Either way it definitely should not be done in secret.

I worry that trying to argue surveillance is entirely useless will do more harm overall because to those 'in favor' of surveillance it's a dumb position.