Typically the longer the bow is, the more leverage you have. that typically makes it smoother drawing. A longer bow typically gives you a better string angle at full draw too. this makes it much more forgiving upon release, or easier to get off the string clean....
i used the word "Typically" a couple times here, because there are shorter bows out there specifically designed to have an excellent string angle at longer draw lengths, that draw just as smooth as a longer bow does...... i have some great photos illustrating this if you are interested.... Kirk