In baking, when should you use 'bake' and when to use 'convection bake'?

Read the manual for your oven - should have cooking guidelines for convection vs regular oven settings. Some ovens will lower the heat from your setting automatically if you are using convection others don't. 

One circulate the air through mechanical means, one does not. Convection cooks quicker so one must adjust cooking times accordingly. With some items like muffins for example, one might not want that air moving for the first few minutes of cooking. One also must know their oven, they are not all the same, even same model. That takes experimentation.