Especially if you end up in water with arm/torso injuries etc your ability to kick can make the difference between getting regular breaths of air vs gulping water drowning in a matter of seconds.
Well... speaking as someone who has been in exactly that situation, along with two broken legs, and a broken back, I can say that it was wearing a lifejacket which saved my life, and made rescuing me possible. Kicking to swim wasn't really going to happen, I was lucky to hold onto a sinking plane while I manually inflated my lifejacket. If you have the forethought to remove shoes before a ditching, much better to have the fore fore thought to wear the lifejacket. Then, leaving your shoes on until you can decide in the water what you'd like to do will be a practical possibility. I'd say that for most of us, it's pretty uncommon to be overflying water warm enough to "swim" in for any length of time nor distance, so planning to be found floating alive is your better plan. If you, or the person(s) in the plan with you were injured, it's a lot easier to help them by inflating the lifejacket they are already wearing for them, than trying to swim to keep both of you afloat.
I have recovered dozens of wrecks, and been in one. the circumstances of every one was different. I learned from all of them. Happily, the sum of what I learned prior to mine was just enough to keep me alive when my student splashed us. Every time I plan to overfly, or land on, water, I consider the possible circumstances and variations, and plan accordingly - there is no perfect rule - other than to wear your lifejacket.