How we cleanup system memory on our macbooks
lots of device support
every time you plug in a device type to xcode you get a duplicate
cd ~/Library/Developer
sudo du -sch .[!.]* * |sort -h
/Library/Developer/Xcode/iOS DeviceSupport was MASSIVE
rm -rf the applicable files
lots of simulator device
cd ~Library/Developer/CoreSimulator/Devices
xcrun simctl delete unavailable
if that doesn't work: this and this