Sleeve diapers are just like pocket diapers - only difference is that their "pocket" is not closed on one end. It is open on both sides so it is a sleeve.
You can add and change inserts to adapt to your baby's absorption needs.
What is also nice is that the step of remove the inserts before washing is taken away. You can add a sleeve with the inserts still inside to the washing machine. The inserts will then agitate out on their own. With a pocket you need to remove them before your wash them.