The problem isn't the Chinese know when you get up in the morning, but it becomes a problem when they know what time General Nuk'em does. Target operations via less then secure IoT stuff are easy enough to imagine, Operations that target a class of interesting are not necessarily impractical either.
What happens when everyone on a base has fit bits and they get hacked? Suddenly there is a lot information about how many people are where when etc that could be actionable intelligence.
Imagine that nice couple that appear to be innocuous embassy employees who help traveling Americans with Passport problems and visa issues; are actually CIA spies. If one of them uses the smart tv in their apartment to call some family back home in Maine at 8pm every night, well you might start to put together they are not a couple at all based on those screen grabs your getting from the TV.
Same thing with mobile phones. They all have cameras now, people take them into secure areas even though they are not supposed to, they take pictures of things even though they are not supposed to. Your foreign operative might drop some QR codes with malicious links around the bars and lunch places near said secure facility and hope to pop phones, grab the picks let AI look for anything interesting..
These ideas might sound like a wild spy novel fiction type stuff, but most of us would have said they same thing about a mass-attack with exploding pagers a couple years ago too!
You can say sure we can control this stuff with policy and what not but the reality is even people who no malicious intent violate policies. That 20-something kids wants to show his buddies the missile he works on snaps a few discrete photos, that former US President 'accidentally' shifts some boxes of classified materials to his garage or a disused room in his resort. People at all levels do stupid stuff with sensitive materials be it paper or electronic. The difference is when sensitive stuff lands on unclassified/insecure electronic systems gets copied or goes missing we way less likely to know.