Clip less pedals.....
Allow for you to use a light and stiff soled cycling specific shoe. For me at least that is reason enough. My feet would be very sore after 5 hours in the saddle using a non rigid soled shoe.
Clip less pedals......
Keep your feet in proper position on the pedals..... Not to far forward and not to far back.

That's the 2 BIG reasons for me to ride clipless....