Sure, it is!

You could, of course, just write it as one amorphous blob were all the UART stuff is inextricably intertwined with all the LCD stuff.

And that would lead you to the state where you can never re-use your own code - or anyone else's code - because the bits you need can never be separated from the bits you don't.

Instead, most people prefer a so-called "modular" approach - where distinct functional parts (like UART and LCD) are separated and provided with clean, well-defined interfaces.

But, if you prefer spaghetti, that's fine.