What scenarios would I use the "Fill a DataTable" vs "Return a DataTable"?  What's the difference?   As far as I can tell they basically do the same thing...but there has to be a difference and I can't zero in on it. 

It's sometimes quicker to return a DataTable:

MyDataSet.MyDataTable MyNewTable = new MyDataSetTableAdapters.MyDataTableAdapter().GetData("param1","param2");

But if the table you're trying to populate is inside a typed DataSet you can't assign the result to the dataset's table:

//Doesn't work:

MyDataSet MyNewDataSet = new MyDataSet();
MyNewDataSet.My = new MyDataSetTableAdapters.MyDataTableAdapter().GetData("param1","param2");

//Does work 

MyDataSet MyNewDataSet = new MyDataSet();
new MyDataSetTableAdapters.MyDataTableAdapter().Fill(MyNewDataSet.My, "param1","param2");

There are no significant differences though