When combined with the other parts (part1, part2, etc.), it forms a valid file that can be installed on a Switch. Cleanliness:
The file might be part of a larger collection of files required to install or activate a particular modification or hack for the game. The presence of "USA" and "NSP" in the file name suggests that it might be region-specific and intended for use on Nintendo Switch consoles. TESVSKYRM--USA--NSwTcH--BASE--NSP-Ziperto.part3...