Q:

Are Unicode Control Characters still in use?

For what I understand control characters were used in Terminals for specific purposes like \n \t \r to break lines and create tabulations. These ones are still heavily used. And their existence make sense.
But the are others that apparently are not used anymore like Set Transmit State(STS), and String Terminator(ST).
For some reason the Unicode standar decided to keep them. For example the latter two (STS, ST) are still in use in modern applications?
What is the reason to keep them in modern times?

A:

One of the major initial goals of Unicode was to be able to unambiguously represent any valid character from any existing character encoding, making it possible to "round-trip" text from another character encoding through Unicode (e.g, ISO-8859-1 to Unicode to ISO-8859-1) without ending up with something different from the original text.
Removing any of these characters from Unicode would have made it impossible to losslessly convert text which included those control characters. Leaving them in place is harmless, and makes it much easier to convert ASCII text to Unicode (since the codepoints between U+0000 and U+007F all align with ASCII).

