Macworld If your Mac is warning that you are running out of storage, you need room for a macOS update, or your Mac simply seems to be slowing down, you may have looked at the large chunk of storage labelled System Data and wondered if you can safely delete it to save space on your Mac . Low storage can cause all kinds of problems on a Mac – you might see warnings that your startup disk is almost full, struggle to install macOS updates , notice performance slowdowns, or in extreme cases even have