A peak lapel is a lapel with an upward point as the lower fabric extends past the upper. It is traditionally more regal then a notch lapel. Cutting peak lapels is one of the hardest tasks for a tailor.
Why you want it- If you are a little more bold then you should look to the peak lapel rather then the notch lapel. And if you’re super-bold then maybe you can check out Tom Ford’s super-wide and super-masculine peak lapel suits.