With running and cycling though, there are plenty of miles where you just put in the time while allowing the mind to wander. I've read where this type of disassociation is actually helpful in distance events because a person could go bonkers thinking of every step or pedal stroke over time.
It's not like form is unimportant while running/cycling (as falling down hurts). Yet once the form or rhythm is there, one can think about life/love/work etc. and still get a satisfactory training benefit by just putting in the miles. And if the rhythm is lost, then you mentally come back to your form and focus on it again.
Haven't seen this written up in swimming; but, at some level do distance swimmers get to the point that the one or two seconds they lose per 50/100 yards while letting their mind disassociate from the pain/task at hand helps the overall experience better while still seeing a training benefit?
And if yes, any guidance about that level of expertise from your experience?