SearchIndexer.exe is the Windows service that handles indexing of your files for Windows Search, which fuels the file search engine built into Windows that powers everything from the Start Menu search box to Windows Explorer, and even the Libraries feature.
It is an essential process for the proper operation of Windows so it is not recommended for removal.
Non-system processes like searchindexer.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that over time your registry suffers fragmentation and accumulates invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues