There are two very common mistakes in freestyle. They both have to do with the “reach”. . 

There are a few reasons why swimming with a freestyle reach is better than swimming like this. Number one is that you pull with bigger group muscles like your back and chest as opposed to just your shoulder when you don’t reach and rotate. The second reason is that you pull more water by reaching further thus you move faster with less effort. Also, in a tight race you will touch the wall faster if you reach to the wall better. 

A common mistake is to cross over the body line when you try to reach. This happens often specially when you take a breath. This will throw your body off balance and you will swim in a zig zag instead of a straight line. 
There are a few reasons why swimming with a freestyle reach is better than swimming like this. Number one is that you pull with bigger group muscles like your back and chest as opposed to just your shoulder when you don’t reach and rotate. The second reason is that you pull more water by reaching further thus you move faster with less effort. Also, in a tight race you will touch the wall faster if you reach to the wall better. 

A common mistake is to cross over the body line when you try to reach. This happens often specially when you take a breath. This will throw your body off balance and you will swim in a zig zag instead of a straight line.