Deploy while debugging/deployment should unlock the screen
When developing with the phone connected via USB, having the screen lock itself is very annoying, and makes app deployment fail.
Some WP7 phone (not the AT&T Samsung Focus) have a "never" screen timeout. However this is for battery and powered scenarios, and you don't want to be manually switching it back and forth all the time. Some of us are stuck with a phone that locks itself all the time. The screen lock also interrupts or prevents app deployment. This makes Visual Studio fail to start the debugging session.
An app deployment should unlock the screen and reset the lock timer to zero.
Sandy Armstrong commented
This is hugely annoying. My device is not PIN locked, so there is no security reason why deploying to the device should not automatically unlock the screen.
Obviously if you have a PIN lock or some other protection on your lock screen, that should block deployment. But not when it's just a swipe. My device does not have an option to turn off screen locking entirely (lumia 900).
Obviously, the device would need to be dev unlocked, so I don't think there's any security risk with this feature. I would assume that Allan's comment is referring to a phone that has a lock screen password. Can you currently dev unlock a device who's screen is locked? I wouldn't think so.
Allan Agerholm Dahl commented
Think about the scenario where I steal a phone from someone else and start deploying apps... Where is the security then?
Nobody looses anything by this feature. Moreover, an annoying need to rerrun the debug session will be removed and that definitely speeds debugging and development.