It is hard to say what will happen, I think there is no certain answer due it will depend on how your images are configured now as well as additional factors that will be specific to your project design, but overall you can use the below as a summary of the advantages of using smart crop that you can compare if the equivalent is already implemented on your images treatment.
1. Image size, Smart crop will deliver an accurate size per breakpoint which will mean that the time in loading the image will be faster
2. Image cache, Smart crop will be cached on the S7 edge using TTLs
3. Correct focus for different viewports, this is usually the biggest advantage.
I think the best way to figure out what will happen is just to do a test, pick up a couple of pages (with a good amount of images), take measurements(first and cache load), and compare the results
Esteban Bustamante