I believe that well-executed turns are an important part of developing good swimming techniques, regardless of whether your goal is OW swimming, pool swimming, or a combination of the 2.
Note that a well-executed turn might be a flip turn, or it can be a properly executed 2 hand touch turn. I'm NOT saying we should all be doing flip turns. In fact unless your stroke technique is nearly perfect I think you are better off refining your stroke, body position, streamlining than learning flip turns.
I watch many swimmers doing open turns where they swim up to the wall, hang on the wall for a few seconds, breathe several times and then execute a very poor push and glide off the wall. Often they push off on top of the water and lack a decent streamlined position. This does not provide any benefit whatsoever, neither for pool swimming nor OW swimming. The swimmer comes off the wall in an unbalanced and non-streamlined position and spends the next several yards fighting the water and simply trying to gain proper body position.
For similar reasons, the argument that 'there are no walls in OW, so I don't push off' doesn't mean much. As others have stated, you don't come to a complete stop every 25 meters in OW so you are not simulating any actual OW conditions by doing a standing or floating start. And again, without the push, your body positioning is poor following the turn, and you've had the opportunity to 'cheat' by breathing several times during the turn.
A well-exectued turn is incorporated into the rythm of the swim, breathing rythm is maintained and correct streamline positioning is maintainted, and a good glide follows the push. The push should be done under the water, not on the surface, and a good streamline position should be maintained. This sets you up for the next length of the pool in a properly balanced and streamlined swimming position, and allows you to maintain your breathing in a properly controlled rythm. During the glide you can focus on a strong kick if you like, either using a flutter or dolphin kick. As the glide begins to slow you should begin your arm stroke just as your body break the surface tension, and you will carry some of your momentum off the wall into your stroke.
Good turns can help you improve both technique and stamina in the water, both of which will carry over into OW swimming performance.
And, don't forget, there are several triathlons with pool swims around the country as well. It sure is nice to be able to take advantage of the walls during these races!