Hi Robyn,

The web client actually does check the document out when you open it for editing. This is to ensure that there is no possibility of lost data due to sessions timing out while working on the document. When the document is saved back into the repository, it is automatically checked back in. You can see this by going to the Documents in Use section of the Activity node in the web client management page and seeing that the documents in question are checked out. 

The difference between this and the explicit check out operation is that the explicit option persists the check out so it remains locked until the user explicitly checks it back in.