In the article "Outside the Box Training: Must be the Shoes" posted on usaswimming.org the author recommends swimming in shoes as a fun and "relatively easy to understand" training technique for swimmers. While I agree that swimming with shoes might be a "fun change of pace", I believe the drawbacks that shoes introduce significantly outweigh the benefits.
First, I would like to point out that the author uses two different terms, weight and drag, interchangeably, essentially implying that they mean the same thing: "shoes also fill with water, effectively creating mini-sandbags on your feet. It's similar to swimming with a drag suit. It's a drag suit for your feet." However, there is a fundamental different between swimming with added weight ("mini-sandbags") and swimming with drag and these terms should not be used to describe the same phenomena. To put it simply, in swimming weight pulls you down and drag pulls you back, which is a very important distinction.
Because of their weight, running shoes pull swimmer's legs down therefore encumbering streamlined body position and balance. Getting out of balance hinders the swimmer's technique. In contrast, swimming with drag pulls the swimmer back without negatively affecting the swimmer's balance or technique. It cannot be overemphasized that wet shoes add weight, not drag.
Another downside of swimming with shoes is that shoes restrict ankle movement and minimize the range of motion of swimmer's feet resulting in a less efficient kick. While it's true that the swimmer must kick harder to swim with shoes on and this has its benefits, the potential impact on technique and reduction in range of motion does not make it a beneficial training tool for anyone who wants swim faster and better.