What will happen if I turn off My Photo Stream on my Macbook?

I have been having issues lately with my phone (iPhone 6, iOS version 9.3.3) where I constantly get notifications saying "Almost out of storage" on my phone. I know where to check which apps are using the most data, and Photos is the highest on my phone. While I do have a lot of old photos I need to go through and remove, I have recently noticed that My Photo Stream is bringing pictures I save to Photos on my Macbook Pro (version 10.10.5, Yosemite) to my phone which makes my phone quickly run out of space. I tried deleting photos to free up space which briefly solved the problem, until I noticed pictures I recently saved to Photos on my Mac are appearing on the phone, eating up all the free space I d just cleared moments before. I want to turn off My Photo Stream to stop this from happening, as I don't want those pictures on my phone, but I'm afraid I will be ending up deleting those pictures altogether. What is the right thing to do to solve my issue?

"What will happen if I turn off My Photo Stream on my Macbook?"

Photos will disappear from devices that have been pushed to those photos.

Most computer use questions can be summarized like this: "Since I can't be bothered to buy an external drive and make a backup, will my stuff be safe?" The answer is always "No". Then the follow up question is "What is the second-best way to protect my stuff without a backup?" Although that is not a stupid question, it is right on the brink.