CSV is good for debugging C/C++ real-time signal processing data paths.

Add cout or printf lines, which on each iteration print out relevant intermediate values separated by commas, with the first cell being a constant tag. Provided you don't overdo it, the software will typically still run in real-time. Pipe stdout to a file.

After the fact, you can then use grep to filter tags to select which intermediate results you want to analyse. This filtered data can be loaded into a spreadsheet, or read into a higher level script for analysis/debugging/plotting/... In this way you can reproducibly visualise internal operation over a long period of time and see infrequent or subtle deviations from expected behaviour.

Agree this is the main use for it