OK, here is a complete guess. And, I am not sure why this is.
But, in the system databases Master, Model and MSDB; autoclose is set to false. In the user databases, all have autoclose set to true.
Now, I am not sure if this would make a huge difference in any office with a small amount of users, but I think most databases are set to have autoclose false by default.
If autoclose is true, then when the last person disconnects from the database, SQL closes the database and releases all of its resources back to the server. When someone reconnects, the database opens and the resources are recommitted. This all sounds well and good and probably is.
But, if the next user is a split second after the first user disconnects, then SQL must make an about face and retrieve the resources. This can and does slow down the database. Whether or not it could make it crash, I have no idea.
