SKPSWI.DAT is used to prevent Software Inventory against a location where it is placed.Full form of SKPSWI is Skip(SKP)SoftWare(SW)Inventory(I).
If you have gone through the SCCM client cache folder called 'ccmcache' (located at %windir%\ccmcache), you would have seen the file SKPSWI.DAT. What is the reason of placing the file in cache folder? CCMCACHE folder is the folder used to store all incoming files deploy against a client. So to prevent software inventory to process the inventory againt the cache folder to avoid 'false positive report', the SKPSWI.DAT file is intentionally placed in CCMCACHE folder.