I agree with Mike "Crop with your Fins", Get It right the first time or at least make the attempt to do this.
Here is my spin on it.
Cropping is one of the traditional darkroom functions that is now emulated through software.
Coming from a background of having worked in a Commercial Darkroom and having one at home developing transparencies and cibachrome, back in the now "monolithic" period of Photography.
I was forever enlarging to 20 x 24 inch paper to crop to 10 x 12 inch size to cater for customers in a particular area they requested. Whether it was to form a potrait or to seperate the bride and groom from the Bridal Party. (This point supports cropping)
You could argue the point of why didn't they ask for that shot to be done that way in the first place. It would have been much easier and less expensive. (This point supports NO cropping)
Sometimes in an attempt to compose a picture you are limited by the surrounding physical environment, it may be best to give the subject the priority rather than composition, (This point supports Cropping).
In the case where you have time and no physical limitations, "Crop with your fins" and try a few more angles. (This point supports NO cropping).
I like to plan my dives to allow the time for good composition of a subject, and this is my aim. Once I achieve that, I do look at what I have done and have another go, if I need to before moving on.
At the end of the dive, you are the one who makes a decision on the display of each of your pictures, if it feels right to crop on a particular picture, DO IT!!!.
I have cropped as much as I haven't cropped, I would say less cropping.
I let the picture talk to me. Let your pictures talk to you.