If a duplicant tries to stand in an airlock they'll get pushed out, which causes them to freeze in place while doing their task. This effect causes deliveries to take a long time due to them being stunned between each delivery . This same effect happens when a tile is built on top of a duplicant while they are doing something as well. It effects all kinds of tasks but some have worse effects than others.
Build an area only accessible through an airlock with a task behind the airlock.