Player Frame Removal is a simple addon that allows you to toggle the visibility of the default player & target frames.
Access PFR's options by:
/pfr or /playerframeremoval
/pfr status - Displays visibility status of player and target frames
/pfr togglepf - Toggles player frame visibility
/pfr toggletf - Toggles target frame visibility
Visibility preference is saved between sessions on a per character basis.