Do I really need to keep CPI file from AVCHD container? CPI files accompany MTS files in AVCHD containers created by camcorders. 
Various posts on video forums suggest that CPI files should be archived together with MTS files, as they contain metadata about the video. Usually it's even recommended to keep the whole structure of SD card. However, it only works fine as long as an SD card contains recording from a single event. In my case, the videos may be completely unrelated and even taken in different years. Therefore I typically store MTS files only, and organize them by date. Sometimes I also rename the MTS files to something descriptive. Maintaining the AVCHD directory structure or even just MTS+CPI files is an extra burden I'd like to avoid.

In my few attempts MediaInfo seems to extract at least as much information from MTS files as it does from CPI files. Frame rate, resolution, bitrate, recording date and time etc. seem to be all saved in MTS. 

So what is the added value of keeping the CPI files?
None of the editing tools I know of uses any files other than MTS/M2TS. Supposedly, these CPI files can be used by a Blu-ray player when it plays the content of a card - which is why the structure of AVCHD media resembles the structure of Blu-ray media - but I never play raw videos from my cards.

I preserve MTS/M2TS files only and throw away everything else. Not once in twelve years I needed them.