It is the best and easiest lens to learn to pre-focus. This skill is one of the keys to using a Leica well. To recap for those who may not already know this (most Leica photographers know this, I'm sure), it is simply to look at the distance to the object you wish to focus on and set the focus on the camera by feel, without having the camera to your eye and without using the rangefinder. Push the tab all the way to the right [directions relative to behind the camera of course] and you're on infinity; place the tab pointing directly down, and you're focused at about five feet. In between those positions, you can learn to eye the distance and set the tab for the focus that is proper for that distance. I did it by first shoving the focus to infinity, then getting the "feel" for how far I should pull it back based on what my eyes were looking at. If you practice this every night for five minutes in your living room, you get very good at it very quickly. Then, as you walk around looking at the world with your M, you can automatically change the focus continuously for whatever happens to catch your eye. Without ever holding the camera to your eye, you are always ready for a quick grab shot. And again, the slight WA focal length aids you here, by covering up errors with its more generous d.o.f. It is perfectly practical to use an MP / 35 'Cron combo all day without once ever referring to the light meter diodes or the rangefinder patch. In fact, I would go so far as to say that any photographer who carefully meters and focuses every single shot is simply not using the Leica correctly.
copied from an article from the web.