The first question you need to ask yourself is:
Why bother? Why is website image optimisation so important?
If you are not even thinking about resizing images then the answer is probably not. You could just serve the original images to your user. It may not have an immediate effect and you will probably get away with it. But what sets truly good websites apart is their attention to detail.
In short, it provides bandwidth savings (meaning fewer servers and less egress data, which is expensive in the cloud) and makes your website faster to load and more responsive (less work for the browser to downscale and paint the image), while also saving your user's internet allowance and battery. The only downside is the added complexity to create and serve these optimised images.
It's up to you to decide based on your particular needs, there are some [other guides][images-guide] that go into more detail. There is a recent movement for providing better online experiences (you may have heard of Progressive Web Apps), and I believe that images play a large role in keeping the experience fast and immersive.