Hourly billing burnt me out. I started on Upwork with the spying software installed. I was desperate for money at that time. But my own methodology when working is to think about the problem, only typing code when I have a good hint about a solution. So for a day of work, I may spend one hour typing code, three hours reading code and the rest of the time thinking hard. But the activity monitor inside the software only picked up the time when you're actively using the computer so, I was always distracted in my thinking with the reminder that I have to use the mouse for the timer to resume.
Now I'm paid a fixed price each month (fairly high for where I'm living). So, wages are not something I think about. But when I try to negotiate other project, I either go fixed, or billed by the day at the smallest. My usual hours for work range from 10am to 5pm, so I bill this amount if the client really wants hourly invoicing.