@ericonline, it is an honor to be called out, especially given the others you mentioned as well. Thanks for that!
Unfortunately, I have little to add as we don't currently use separate environments or service accounts, though the service account idea is on my radar. Full disclosure: the company I work for is pretty small and I am the sole tech/data employee. As such, I have only used my company account to create things in PowerApps as it was just easier to do so. 
That said, I will offer one practice that I have been using in lieu of environments. One way I track what level of access the app is by the color of the app icon. Pretty simple but it is decently effective. For example, our field supervisors get red apps, our office apps are blue, and test apps are yellow. Incidentally, I do a similar thing with our PowerBI reports by using color schemes.
I also have a similar practice to @Anonymous when it comes to publishing apps. I found that things would get a bit funky for our field employees when I would make changes to apps and not publish them. So I started the practice of having parallel test apps where I can develop changes or add features at my leisure and then replace the production versions when things were ready to go out. This gives a bit better version control as well and could make for easily segmented test and production groups if needed.
Great topic and I look forward to learning from what others are doing!
