I do this a lot. The only con I can think of is that you have to take extra steps to ensure people don't load random software or change settings. I resolve this by making sure the app takes the full screen, no keyboard, and the app has no easy way to exit to the desktop.
Some will argue the instability of Windows and I would agree if it was 20 years ago, but Window 7 and 10 are very stable as long as you don't install unstable software. In other words, if it is an HMI, then let it be only an HMI and don't let people install any random bits of software. Keep it off a network with internet access and you won't have to worry about Microsoft installing constant updates.
As for pros:
- No more proprietary hardware to have your machine down when it fails and you need to find an exact replacement. Especially when it becomes obsolete
- Many software options. If a particular HMI software doesn't do what you want, the majority of the time you can change the software without buying new hardware
- More hardware options that let you select the amount of processing power you need. I have a few installations where the same HMI applications runs on a panel PC for general use and a tablet for maintenance use.
- Gives you the choice of installing things for features you need such as a database server or remote access software (VNC type software)
- IT is generally more willing to provide help in a pinch because they should be familiar with PC hardware and Windows OS
