Note that printf() is a generic function for producing generically formatted text messages.

When doing communication, it is quite common that the protocol have very struct rules for the messages, in case strcpy(), or strcat(), or memcpy(), ... may do what you need. And if you need to send numbers as ASCII character sequences, it's quite easy to write a small function that converts the value of an int into a string of digits.

By the way - depending on compiler and implementation, printf() may be polled. Or it may fill a buffer for interrupt-driven transmission, but hang in a polling loop if the emitted data is larger than what fits in the buffer.