There are a few potential disadvantages to using user-defined functions in your code:

1. Performance: Using user-defined functions can have an impact on the performance of your code, especially if you are calling the functions frequently or if the functions are complex. This is because each time you call a function, the interpreter has to jump to the function’s code, execute it, and then return to the calling code. This process can take some time, especially if the function contains a lot of code or if it is called many times.
2. Readability: In some cases, using too many user-defined functions can make your code less readable, especially if the functions are not well-named or if they are difficult to understand. This can make it harder for other developers to work with your code, or for you to come back to it later on.
3. Debugging: Debugging user-defined functions can be more difficult than debugging other parts of your code, especially if the functions are complex or if they are called from multiple places in your code. This can make it harder to identify and fix problems in your code, and can slow down your development process.
4. Reusability: While user-defined functions can be useful for reusing code, they can also make your code less reusable if they are too specific or if they rely on other code within your project. This can make it harder to use your functions in other projects or to reuse them in different contexts.

Overall, while user-defined functions can be a useful tool for organizing and reusing code, it is important to use them wisely and to consider their potential disadvantages when deciding whether to use them in your projects.