Most emulators (Citra, Panda3DS, Lime3DS) cannot run encrypted ROMs directly. Therefore, many users prefer a "decrypted" or "CCI" set. Additionally, "trimming" removes dummy data (empty padding used to fill cartridges). A trimmed ROM is smaller but functionally identical.
Unless you are a preservationist for the Internet Archive, you only need the highest revision number (Rev 2 > Rev 1 > Rev 0). 3ds Complete Rom Set Size
~652 GB after removing duplicates and region-redundant files. Most emulators (Citra
: Even if your SD card is large enough, the 3DS has a hard limit of 300 titles on the home menu. Users with large collections often use 3DSBank to swap between different folders of 300 games. Rev 1 >