Adding to Seaman, there are advantages to ankle carry over pocket carry. If your job requires you to sit for most of the day, an ankle holster will be far, far quicker than a pocket holster. In addition, if you are on your back, say, you were knocked down in a fight or something, the ankle is a very easy and natural place to draw from.
The biggest drawback to ankle carry is that it requires you to come to a complete stop while drawing. There is no way to reliably draw while moving, and one of the most important things to do, if you can, in a shooting situation is to move while drawing (since being stationary while drawing makes you a sitting target, and puts you at a tactical disadvantage).
That drawback is enough for me to not recommend ankle carry as a primary carry method unless you are seated for most of the day. Great as a backup, not so much as a primary.