Many devs on Upwork report having to install either a Chrome plugin that tracks all browsing activity or a full-on desktop monitoring suite that tracks everything they do while they are "on the clock". It's Orwellian.
I never used the service, but I guess this is to avoid extreme cases. I guess the record are used in case of litigation, not to meet a fixed level of performance (aren't Upwork workers independent contractors, anyway?) .
Also, saving the work methods of people certainly has value for later analysis, but I'm not sure how much it breaks workers' intellectual properties.