a. I can ride in any type shoes - cycling, tennies, sandals, street shoes, or hiking shoes.
b. The staps hold the foot as securely to the pedal as clip-ins and are easy to get out of.
d. No need to carry another pair of shoes on tours for walking, hanging around the camp site, etc.
e. For a quick ride, there's no need to switch to special shoes.
f. I can walk through dirt or mud without having to clean out cleats.
I attached thin metal plates to the pedals of a couple of my bikes, making a platform pedal for riding comfortably with thin-soled shoes or sandals.
Riding without clip-ins is certainly possible -- it was done for more than a hundred years.