Complex sentence: When Tarantino began editing the film, he and Weinstein agreed to split the film so Tarantino could edit a fuller film, and Weinstein could have films with reasonable running times.
Split into simpler sentences: When Tarantino began editing the film, he and Weinstein agreed to split the film into two. With the approach, Tarantino could edit a fuller film, and Weinstein could have films with reasonable running times.