If you need the grated rind of a whole lemon, it is worth using a grater. However, when you are cooking small amounts, you will often require ½ tsp of grated lemon rind. I don’t like having to wash a grater for that small amount.
You can easily accomplish the same goal with a very sharp knife and steady hands, or a vegetable peeler. If using a knife, slide the knife along the lemon, just under the peel, to cut off a small amount of peel. With a vegetable peeler, simply draw the peeler along the lemon peel with a bit of pressure. Both methods will provide a small piece of lemon rind.
Now, simply slice it very finely one way, then again the opposite way. If you have more than one piece of peel, simply stack one piece on top of the other before you slice. The resulting finely diced lemon peel will work exactly like grated lemon peel … without the extra tool to wash, or taking room in the dishwasher.