When baking, room temperature ingredients work best, particularly the fat, eggs and any liquid you may be using, except when making pie crusts and pastry or other recipes, which call for chilled fat.  

BUTTER: Creaming calls for ROOM TEMPERATURE BUTTER or fat, which is 68 to 70 degrees F. I actually like to start out with a little cooler than room temperature butter -- around 65 degrees F. It helps me to keep the butter from softening too much during creaming, producing the best results. When creaming butter and sugar, if the butter is too cold or too hot, it won't be able to form and hold air bubbles. If the eggs and liquids are cold, the batter will curdle when they are added to it. Likewise, if any of the ingredients are warm, the creamed fat in the recipe will melt and will lose air bubbles. In all cases, the baked cake won't rise very high and will be too dense.

EGGS