In Excel 2010 you can add new columns to the powerpivot data model, add a title, change the data format, change a title letter to capitals etc without forcing a complete recalcualtion of the whole workbook unless you actually request it. These changes make no difference to the workbook, but it seems that every tiny change in Excel 2013 trips a full recalcuation. To get round this you have to hit escape in the workbook for every pivot table, of which I have 20. So in order to add a new calculated column (note "new" so it is not involved in any pivot table) I have to insert a column and hit escape 20 times, next add my formula and hit escape 20 times, next give it a title and hit escape 20 times and maybe change the date format from dd-mm-yy to dd/mm/yy and hit escape 20 times. It's enough to make you suicidal if you have a lot of building to do.
This is just bad code as the model should be able to tell if a change has any affect on the workbook. Or just have the abilty to turn it off like the defer layout check box. I really wish I had never "upgraded"