Its a very good article and all points are worth considering. This got me thinking however.
What if we are new to the game? have High goals or have decided to work on swimming, maybe a weak area...
bottom line here, look for and explore all your resources, and use them!
One of the reasons I personally have for swim focus periods is the issue of quality training. particularly when high intensity training is on. Its tough to run and bike hard. however swimming hard and biking (or running) hard seems to work for many without a drop in the quality or performance in there training. this makes swimming more "doable" when the running or cycling intensity increases.