i've been downloading ableton live since version 2 came out, and i still can't fully figure out what the session view is used for
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It's for DJ'ing in a "Live" situation. You load up tracks/samples/clips in those slots and hit play and as long as you have everything warped properly it will play them on beat with whatever tempo you have it set at.
People who produce electronic music also use it as a way to perform their music live since it's almost impossible to play those synths live the way they have made them sound.
I'm against people who DJ with it and nothing else but a midi controller though. It takes a lot of the skill/craft/audience interaction out of being a dj.
I use live because of its warping capabilities which make it easy to make edits of tracks for me to spin and make mashups, etc.