Parts of apps
SourceKitServiceXcode build tools
◐ Close the app instead
Builds code or understands it for Xcode.
What it is
The compiler and services Xcode runs while you build, index or preview.
Why it might be busy
During a build or after opening a project. Usually until the build finishes.
If you close it
The build or code completion stops. Stop the build in Xcode instead.
The verdict
◐ Close the app instead. A part of an app. Closing it alone breaks something, so close its app.
In Activity Monitor
SourceKitServiceXCBBuildServiceswift-frontendclangldxcodebuildswift-buildIBAgent-iOSibtooldXCPreviewAgent
From Procession’s guide, in the words the app shows.