Exactly.

As an hourly worker your are paid for your time working.

As a salary worker you are paid to complete assigned tasks.

When I managed technical professionals I actively encouraged people to go home when they finished everything they could in their project queue. I'd rather promote incentive to get the work done sooner rather than drag it out to make sure they looked busy for 40hr a week. I once had a manager of hourly people complain to me about my people leaving. I asked if they could cite a recent failure to deliver, they couldn't. Likewise, when shit hit the fan, I fully expected my people to come in early, stay late, and work across hourly employee shift schedules until the problems were resolved.

I also think that good professional salary workers never really stop working. I've had some great work ideas at 9:00 PM in the shower.