Q: can I delete photos from the main computer without losing them in iCloud photo library?

I'm thinking of setting up iCloud photo library as a way to save space on my Macbook air. But once uploaded to the cloud, can I delete my photos library stored on my mac without losing them in the iCloud library?

The photos will stay in iCloud, if you delete the library on your Mac,  but after deleting thePhotos  library from our Mac, you can only access the photos in iCloud using the web interface at www.icloud,com and you cannot use the Photos for Mac app any longer to manage the library.

Instead of deleting the library on your Mac completely, consider to enable the option "Optimize Mac Storage".  Then the full, original versions of your photos will be stored in iCloud, but your local library will only contain smaller, optimized versions. You can reduce the size of your library to 10% of the original size this way, and still use the Photos.app on your Mac to browse your photos.