Just a few notes:
* Accommodation will be cheaper (no holiday season, and Eastern Germany has lower costs of living in general). The city is currently extending their local transportation networks into surrounding small towns, so there should be more to choose from.
* The area is outside the city, but not remote. Trains from Berlin and from Leipzig-Halle Airport stopped at Messe Leipzig in the past (not sure whether this is still the case), which made the journey from Berlin even shorter than the 1h 15min it takes now. It is also a popular stop for cheap long-distance buses.
* I am personally not aware of halls that can hold thousands of people in the Congress Center itself like in Hamburg, but I am not sure as I have not been there in a while. Here is a hall overview: http://www.ccl-leipzig.de/raeume-technik/raumuebersicht/ I guess CCC would need to make use of the actual big exhibition halls as well for the really popular talks if they don't exist ( it would be quite cool if they could use just one of them ). Well, I always wanted to have a CCC cardboard stool (Papphocker).
* Leipzig has a vibrant cultural, art and alternative scene. Google "Baumwollspinnerei" or "Viktorianisches Picknick / Wave-Gotik Treffen".
* A start-up scene exists, but it is not as developed as in Berlin and Hamburg. In general the city feels less international (while still being home to some international audience e.g. due to having the trade fairs, the said creative people, a big university and three Max-Planck Institutes)).
* Architecture: The hall of the main station is the biggest one of a terminus station in Europe. Visitors tend to like the "Leipziger Passagen" that traverse the inner city. Völkerschlachtdenkmal. And (just saying ;) ) the computer science and math faculty of their university resides in a newly built landmark temple of glass and light with quite an interesting history ("Paulinum").