In Photos, can you crop and scale original to save space?
Any edit will always increase space used, as it will keep the original in Masters &amp; add a new edited version. 

It's the 'safest' method which is why I presume it's done that way.  

If you want total control over your pictures, you need a more pro-oriented application.

Having said that - my own workflow only uses Photos as a 'show it to people &amp; carry it on the phone' structure. All my real work I do in Photoshop, ViewNX-i etc... but the downside of that is I end up with far more safety copies &amp; work in progress/files with different icc profiles etc than I would if I just used Photos.
One picture can end up having 1GB of variations, + backups in 2 other locations.