The short answer
Usually, after a check. Might hold something you care about. Look inside before removing it.
What is it?
Simulator runtimes are complete copies of iOS, watchOS, tvOS or visionOS that simulators boot from. In recent Xcode versions they are downloaded separately from Xcode, stored as disk images and mounted under /Library/Developer/CoreSimulator/Volumes. Each runtime typically takes 7 to 10 GB, and older ones stay installed after you update Xcode.
Full iOS/watchOS/visionOS system images, 7-10 GB each. Keep the one you test on; Xcode can download others again.
What happens if you delete it?
Xcode can download a removed runtime again from Xcode › Settings › Components (several gigabytes per runtime). Simulators that used it become unavailable until it is reinstalled.
How to remove it properly
Remove runtimes in Xcode › Settings › Components, or run xcrun simctl runtime list and then xcrun simctl runtime delete <identifier> in Terminal. These are mounted, system-managed disk images: do not drag them to the Trash, and expect the deletion to be permanent.
Use the tool’s official command: xcrun simctl runtime delete <runtime>
Before you delete it
Keep the runtime you test on day to day, and older ones only if you support those OS versions.
How MoreRoom helps
MoreRoom recognises this item and labels it “Review first”: it shows what’s inside, its size and last use, so you can decide. Nothing is removed without your say, and everything goes to the Trash first, with Undo.
When the tool is installed, MoreRoom runs its official command for you (xcrun simctl runtime delete <runtime>) instead of deleting files — and tells you that this step can’t be undone.
Frequently asked questions
Can I delete simulator runtimes in CoreSimulator/Volumes?
Usually, after a check. Might hold something you care about. Look inside before removing it. Xcode can download a removed runtime again from Xcode › Settings › Components (several gigabytes per runtime). Simulators that used it become unavailable until it is reinstalled.
Will Simulator runtimes come back after I delete it?
Yes. Xcode can download a removed runtime again from Xcode › Settings › Components (several gigabytes per runtime). Simulators that used it become unavailable until it is reinstalled.
How do I remove Simulator runtimes properly?
Remove runtimes in Xcode › Settings › Components, or run xcrun simctl runtime list and then xcrun simctl runtime delete <identifier> in Terminal. These are mounted, system-managed disk images: do not drag them to the Trash, and expect the deletion to be permanent.