"Joe goes to the gym three times a week" is a fact.
"Joe's network activity originates from a gym on the following schedule" is not only at least an equivalent fact, in practice it's far superior to the simple case. It can give you subtleties [1], it's less susceptible to subterfuge [2], it gives you actionable evidence of specific occurrences, etc.
Consider the CIA doesn't use meta-data to target hellfire missiles because it's less identifying than actual data. They use it because it's far better.
[1] Joe never goes to the gym on Saturday. Joe goes to the gym more during the spring than the winter. Joe almost never misses a day when Sally is at the gym. Joe and Sally nearly always leave at the same time.
[2] It's trivial for someone to say they go to the gym on a schedule they don't. It's not even too difficult to get a second or third party to fudge, embellish or outright lie on their behalf. It's much more difficult to get a second or third party to help you make your device convincingly take the claimed routine, without you creating any conflicting meta-data that gives up the ruse.