What is the purpose of "Mic to Headphone" found under the new performance flyover screen?
When using headphones, it's nice to have your voice heard in them, especially if they do a good job suppressing external noise. In those cases, make sure "Mic to Headphone" is On. On the other hand, if you connect your device to a PA system or anything that uses external speakers, you may want to stop your voice from going to the speakers.
For example if your microphone picks up the amplified version of your voice, a feedback loop may be created. In those situations, either make sure you use proper microphone techniques to avoid feedback, or turn "Mic to Headphone" off.
Note: When using VoiceJam on a device with no headphones connected, the mic will automatically be muted in its internal speakers to avoid feedback.