Originally posted by MJKoski Aspect ratio of m4/3 is the key difference. 4:3 is far more useful than 3:2 which is not wide enough for panoramas but also fails with scenes containing tall subjects. K-1 is almost useful in emulating 4:3 with maximum up/down sensor shift. Cropping to certain aspect ratio in post is totally different than composing in proper aspect ratio. Former equals the case "Failing to plan is part of the plan".
I wouldn't call it "far more useful"... that's a Ken Rockwell-style hyperbole...
I routinely crop my pictures when developing from RAW, and use the ones that I'd call "most used aspect ratios" ("used", not "useful", it's a convention), that is 16:9, 3:2, 4:3 and 1:1.
I guess one picture in 10 (maybe even less) ends up in a 4:3 format, very few in 16:9 (mostly landscape) and I think about the same (little) amount in square format.
4:3 is IMHO a little easier to compose into, since it's more static than 3:2, but I almost always feel that - unless the picture is in landscape orientation and the subject occupies a small portion of its length - 4:3 gives the subject far too little "breathing space", and 3:2 is often a much more elegant solution.
Bottom line is, both a.r. are useful, it's just a matter of knowing when to use one or the other.