Today I discovered that there is a significantly large group of additional control codes, called C1 control codes, spanning from U+0080—U+009F (32 characters). I think that it's an interesting fact that there is such a large part of the single-byte character set (latin-1, latin-2, etc.) devoted to controlling sequences. Knowing how useful the C0 controls may be I wonder what uses do the C1 have? Reading Wikipedia I see that it's mainly about some terminal-related quirks. Is there no more important C1 control keys use?
The link to wikipedia in your question already explains a lot on the topic.
On Linux the OSC codes implemented by xterm (which most other terminal emulators follow) are defined in its ctlseqs. Some OSC codes are also supported by tmux.
The most recent addition to "what can it be used for" is OSC 52 which gives the application running in the terminal access to the system clipboard.
Codes supported by the Linux console are defined in