Stoping wordpress creating large and medium image _ Bad Idea

I upload a 1200×800 at 67 kb and wordpress makes a 1024×683 at 140kb so a 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 Astra to use so 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.

I also see that Astra is creating its own size at 768×512 and 86kb for the same image independently of wordpress. I am happy to keep making this file as its not a much bigger kb than my original.