If you don't have measurable inputs and outputs (i.e. Tickets, service requests, widgets, cases, etc), you typically lose productivity. Not necessarily because of the employee, but also because of managers who don't function well with out of sight people.
Personally, I think in many cases you'd get better outcomes out of sending people home at noon on Fridays than having them telework.
Of course if you're not giving employees anything to do, you'll get reduced productivity. That's also true if you force them to sit in a chair in the office and do nothing. If you can't come up with anything for them to do (slow season, sales pipeline stalled) maybe let them pitch ideas for things they'd like to work on and give the ok on some.
Either way, if they have something to do and you keep in touch with them on how things are going, things should keep moving even without specific granular measurements. But why not use tickets or tasks or something to make it visible?
> also because of managers who don't function well with out of sight people
Those people probably shouldn't be managers, at least not working with remote workers. Communication is critical. A remote team should feel like they're communicating at least as much as an in-office team, if not more.
My viewpoint is exactly that, my viewpoint. I make it well known that when I am working from home it is likely because I have 9-5 errands to run, but I will be available throughout the day.