With television still in it's infancy, the vast majority of television shows and programs made between 1947-1950 were done in kinescope (see my "What's Kinescope" link for more infomation), which was the technological equivalent of film vs. digital today. Kinescope itself was literally about as thin as cheesecloth, and therefore not known for longevity (hence the reason so many early television programs are lost to us today). On top of all of that, television virtually only existed in New York City, where programs done in kinescope could be broadcast to the largest audience.
Lucy and Desi, however, knew they did not want to use kinescope, but film, and they wanted to do the show in Hollywood (closer to home, in Chatsworth, CA). Therefore it was decided that they would film the show in front of a live audience, chiefly because a) a show on film would have infinitely better longevity and quality, b) would reach a larger audience, and c) Lucy was better in front of a live audience (which she had learned doing "My Favorite Husband").
A television show had never been done on film, much less in addition to a live studio audience. At the helm of pre-production, Desi proved to be an impressive innovator of technology. His first order of business was to figure out how to do the show live while filming it. And for that, he turned to the best in the business: Karl Freund.