@StephenDarlington 's answer is very clear.
The author updated the article for Xcode 7.0.1 in Oct 2015.
~/Library/Developer/Xcode/DerivedData
The Derived Data folder here contains all of your project’s
intermediate build information, index and debug/release built targets.
You will generally delete this data when you observe peculiar
behaviour like improper indexing or slowness of Xcode. Deleting all
folders(Not derived data folder itself) from derived data will just
make all your projects to be recreated when you build again;
rebuilding will be bit slower.
Tip: Open Window > Projects
. Select the desired project and click
the Delete button next to the Derived Data path.
~/Library/Developer/Xcode/Archives
All your targets are kept in archived form in Archives folder.
Before you decide to delete contents of this folder, here is a warning
- if you want to be able to debug deployed versions of your App, you shouldn’t delete the archives.
~/Library/Developer/Xcode/iOS DeviceSupport
iOS Device Support folder creates a subfolder with the device
version as identifier when you attach the device. Most of the time
it’s just old stuff. Keep the latest version and rest of them can be
deleted (if you don’t have an app that runs on 5.1.1, there’s no
reason to keep the 5.1.1 directory/directories). If you still have a
device running a particular version, the directory will be recreated
by Xcode when you attach the device. And, no, this has nothing to do
with simulator.
Caution: You’ll want to be careful when removing files from inside
/Library
and /Users/<yourusername>/Library
as deleting the wrong
files can cause applications, and even the OS, to misbehave.
~/Library/Developer/CoreSimulator
Core Simulator folder is familiar for many Xcode users. It’s
simulator’s territory; thats where it stores app data. It’s obvious
that you can toss the older version simulator folder/folders if you no
longer support your apps for those versions. And, it’s safer to use
‘Reset content and Settings’ option from menu to delete all of your
app data in a Simulator.
Tip: [[[NSFileManager defaultManager]
URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask]
lastObject]; will print the full path to document directory folder.
Note: As we know, simulator location was moved from
~/Library/Application Support/iPhone Simulator since the Xcode 6. So,
if you have not cleared out this directory, have a check.
~/Library/Caches/com.apple.dt.Xcode
Caches are always safe to delete since they will be recreated as
necessary. This isn’t a directory, it’s a file of kind Xcode Project.
Delete away!
~/Library/Application Support/MobileSync/Backup
Additionally, Apple iOS device automatically syncs specific files
and settings to your Mac every time they are connected to your Mac
machine. To be on safer side, it’s wise to use Devices pane of iTunes
preferences to delete older backups; you should be retaining your most
recent back-ups off course.