If you haven't experienced it yet, I would suggest to take one fin off while underwater, and see how much slower you swim and how much more gas you are breathing.
As a Divemaster in training, one of the students I was following undersized fine straps broke on descent and his fin wouldn't stay on without it. I traded with him and spent the rest of the dive following behind the instructor and students swimming with one fin and carrying his. It was hard slugging. Lucky I had a 120 cf tank as I used way more air than normal. Got to practice several one finned kicks, none were that great.
On a fun dive if I ever lose a fin I'll be either heading back up or examining a very small section of Reef/Wall for a long time.