Use when the size of the code is large and you want to fix bugs efficiently.
USB print debugging is convenient because it can be used without the need for additional hardware. However, the code needs to be modified and compiled. Also, it cannot be used in performance-sensitive applications.
In such cases, I debug with J-Link/J-Trace and Ozone. Ozone is a powerful debugger and I use it a lot. And, I also use RTT for print debug. RTT has little effect on performance and pausing the code in the debugger has no side effects.