Better chance of birthing without needing assistance with vacuum for forceps. Better sense of satisfaction and accomplishment. Every woman's labor follows its own timetable. Many of us are out of practice at listening to our body's signals. So don't worry if things seem to slow down and you don't feel a need to bear down yet.
Upright positions use gravity to help bring the baby down.
You may also just need to soothe out any last minute worries you are carrying around with your. Ask yourself what you need to feel ready. That's part of letting go. Know that if there is a reason why you should not wait, your caregivers will tell you. You can always change to directed pushing if you have to - everyone knows how to help you do that.