Citrus zest can add the bright flavours you want in many dishes, like risotto or salad. However, preparing the zest beforehand as part of your mise en place can have a huge impact on the taste.
Image from grongar
When you use citrus zest, what you're really after are the oils in the skin. The oils are what bring the flavour and aroma of orange, lemon or lime to your dish. If you zest too far in advance, the peel sits out and the oils are lost into the air. So, even if you have a lot of citrus to grate, do it just before you need to use the zest to preserve the fresh flavours.
Tips for Cooking with Citrus [Bon Appetit]