Welcome to Android Central! If you're using the Windows Explorer Import Pictures/Videos option, then don't -- it can't tell the difference between photos that are important to you and junk cached images that apps create and use. I suggest manually selecting the photos you want to copy using Windows Explorer, then dragging and dropping them to the computer hard drive. Or just make sure Google Photos backup is turned on -- you get unlimited storage or your photos in the cloud at original resolution. Once everything is backed up to Google Photos in the cloud, you can use the Free Up Space option in the Google Photos app to automatically delete all locally saved copies of those photos, since they've been safely backed up to the cloud.