I shoot digital, and there are times when I want to be hands on with focus and aperture. One of my favorite lenses is a Tokina EL 28mm. I have a reverse ring that I attach to the filter ring. What the reverse ring does is allows me to shoot macro by reversing the lens. I can switch from standard to macro in seconds with this setup.
Different lenses have different characteristics. My old Industar 50-2 has wonderful bokeh and works well as a Macro lens when teamed with extension tubes.
Using those old lenses forces me to slow down and become more deliberate in the process of taking photos. Instead of coming home with 150 photos, I end up with 30 to 40 photos. There will be less throwaway images when using manual lenses. There will be some spoiled images because I didn't get the focus right, but that's OK. The remaining images are framed much better.
My next lens will be the Rokinon 14mm 2.8. It's a manual lens.