Depending on what type you have it will be better suited for ale yeast that are happiest in the low 60's you could turn it off and let it sit at room temperature if you needed something higer than 65. The temp controller is the most exact way to maintain temp though. The important thing is to do what makes you most comfortable. Either one will be fine it just depends on how much you worry about the minutia. IMO, go with the controller, I'm sure by the end of the day you'll have 6 opinions one way and half a dozen the other