Certainly purge all unused stuff, but if your model is large due to the nature of the model, Chris Fulmer had a great tip regarding using scenes to handle large models. It is a very creative way to deal with this issue. Watch the first part of the Basecamp Video, link below http://www.youtube.com/watch?v=r9_F-bSGrKs There are also great tips in the rest of the video, but the first part might be helpful.