With NYC, you can maintain an unlimited number of cookbooks (up to 32,000 recipes in each), giving you capacity to handle an unlimited number of recipes. With NYC's ability to search, meal plan, dupe check, and print recipes across cookbooks, there is really no need to keep all your recipes in one cookbook.
In fact, there are many advantages to using smaller, multiple cookbooks. Large cookbooks use lots of RAM for cookbook indexes and this slows NYC performance. Also, the number of recipes per category can be very high with a large cookbook, even with 200 categories in use, making it difficult to find recipes. About 5,000 to 10,000 recipes per cookbook is a reasonable maximum size for good all-round NYC performance on a modern PC (say, 300 MHz and higher).
Multiple cookbooks also give you more flexibility in hierarchy and organization. For example, if you kept all recipes in one cookbook called MYCOOK, you might have a category called “desserts” with cookies, cakes, and pies in it. With multiple cookbooks, you could have a cookbook called DESSERTS with separate categories for “cookies”, “cakes”, and “pies”. If you are one of those power users with a collection of 100,000 recipes, you might even want an entire cookbook dedicated to COOKIES, with categories like “chocolate chip” and “oatmeal”.