In my quest to find out why Xcode is so big, i found out that a lot of the space is taken up by the subfolders to the Developer>Platforms>iPhoneOS.platform>DeviceSupport folder..
Since I am (apparently) only allowed to develop for the last of them in Xcode, can I safely remove the rest (in this case 3.0 to 4.2.1)?
Same question regarding the subfolders of Developer>Platforms>iPhoneSimulator.platform>Developer>SDKs..
Yes you can remove SKDs prior to 4.0 in Developer/Platforms/iPhoneOS.platform/DeviceSupport it's just old stuff.
For the subfolders in Developer/Platforms/iPhoneSimulator.platform/Developer it's all the devices version that you will find in iOS Simulator in the menu Hardware>Device>Version. It can be sometimes usefull to keep them to test retrocompatibility (But remember that a test on a real device is still better). But if you want you can also remove these SKDs.
来源：https://stackoverflow.com/questions/5302789/can-i-remove-previous-versions-of-iphone-support-in-devicesupport-folder-in-xcod