In reply to Tobstar:
Psychology. Does the prospect of 20-30cm longer falls have any adverse effect on your climbing.
If you're confident climbing above bolts and taking marginally longer falls when working routes then there is no point in having a lot of shorter ones. The rope will generally run a bit smoother with longer ones.
In some situations falling another 20-30cm will absolutely matter, especially on shorter routes or those with ledges. However, if you're climbing in the 7s and not the 5s, most of the time there will be no safety reason to use the shortest draws.
Having had another think about this, all my climbing partners who consistently climb high 7s almost exclusively use medium and long draws.
However, like most things with climbing and gear, it will ultimately come down to personal preference