Lightroom CC storing to my hard drive

Admitingly I have not organized my photos in Lightroom well at all over the past year and a half since I begain using Lightroom CC. I work off a Macbbook Pro that has 256GB of local storage space. Currently Lightroom CC is taking up 170GB of space locally on my hard drive. This is obviously way too much for 1 application and creating a sluggish work flow. 

My question is why is Lightroom CC storing to my computers hard drive? How do I purdge these photos from my hard drive without loosing the raw files in my Lightroom? Also, what can I do to keep this from happening in the future? Is this a issue of poor organization in my Lightroom App or a incorrect defult setting that has them being stored in my Lightroom in a way that is creating duplicates?

Thank you for any and all advise.