Lightroom using a lot of memory on computer

Even though I have an external hard drive where I am saving all of my edited photos, Lightroom is sucking up around 4-5 GB of space on my computers main hard drive every time I use it. I'm only editing 5-20 images at a time. What am I doing wrong here? I am worried I am not going to be able to use this very long due to loss of computer hard drive space.  
I have a Lenovo Yoga