WordPress resizing images bigger than they are

I edit my images to 1200×800 in photoshop to around 70-100kb then upload them through media upload but when wordpress creates the extra sizes the image files are larger than my original uploads for a smaller image.
I upload a 1200×800 at 67 kb and wordpress makes a 1024×683 at 140kb so smaller image but bigger kb.
I have read about this behaviour and a simple fix to stop it is to put 0x0 in the media uploads setting for medium and large. So as they are not there for my theme to use then it uses my original 1200×800 67kb image instead.

My question is will doing this have an adverse effect on my sites speed ranking results in any way.