The most immediately useful functionality for many will be Neptune's ability to work as an Antares Auto-Tune-style pitch adjuster. This will save Record users from having to use third party audio editors and plug-ins to fix vocal takes, and will also allow for the creation of extreme, T-Pain-style Auto-Tune effects.
Neptune can also works as a more basic transposer, for pitch-shifting tracks up or down a set number of semi-tones. Finally, the synth will also work as a voice synth for creating new harmonies for your vocals via MIDI input, or to change the melody of the original part.
If you can't wait to get your hands on this cool new Record feature you can sign up for beta testing here.