title: usage of WriteConcern in mongoDB
body: <p>I am reading <code>WriteConcern</code> at mongoDB wiki but it's not clear for me. I have a question! what is it and when we must use of <code>WithWriteConcern(WriteConcern.Acknowledged)</code>? 
  what is difference between:</p>
  
  <p><code>WithWriteConcern(WriteConcern.Acknowledged).InsertOne()</code>
  and <code>InsertOne()</code> and which one is better that we use?
    please explain simple.</p>