I had been to several DSM classes with well known teachers and one thing I realized is I was getting shoulder and back pain from shoving everything thru a small space. My LQS started offering LA training classes in order to rent their machine. I fell in love with the LA, since it is easier, as DebraK says," to run the needle over the quilt, rather than guide the quilt under the needle." So I rented until we moved to a new house, where we had room for a LA and I was unable to find a machine to rent at the time. My DH said we could buy one.
The Sitdown machines still require you to push the quilt under the needle, but you have room to guide the quilt under the needle and more surface to support the quilt.