Although the Lumix G series allows me to pack 35mm equivilent 14-400mm lenses, a camera body, filters, spare batteries etc. in a tiny camera bag that looks as though it is a normal tourist bag not a pro-style hefty camera case there are times when you just want to take one camera and one lens.
My G3 may be a couple of years old but it is tiny, I am looking at the GX7 but don't see the need to upgrade right now. So stick the 20mm f1.7 lens on it and I can put the G3 in my pocket. The lens is tiny, really sharp and has a lovely bokeh (out of focus parts) plus a generous maximum aperture.
The 35mm equiv. of 40mm focal length is just about perfect. The Micro 4/3 has a different, more square, format than the 35mm format so this is a perfect "standard" lens meaning it captures on camera roughly what the eye sees. I can wear this under a light jacket without anyone knowing I have a camera and then quickly take photos and replace it. Perfect compromise.