Yep, I set it to high (less picky, more peaking on less contrasted, softer images) when using vintage lenses wide open, and low (more picky about what it highlights) when using sharper or stopped down images.
LOW setting by default is a dark blue and works best on vintage lenses on soft, low light images. HIGH is a light blue/cyan and works best on super high contrast, high detail shots.
If you use LOW in ETC mode on a high detail image the whole screen when zoomed in to 10x preview will be all blue peaking and you can't see the image at all. For outdoor high contrast stopped down images I have to set it to HIGH. For indoor dark scenes, I have to go to LOW to get any peaking to show up at all with my speed boosted OM 50mm f/1.4
Just my experience with the GH4's peaking settings.