Would resizing images within CSS affect page load performance?

In one of the objectives in this course, specifically the about page exercise: We are instructed to select an image via an assigned .profile-photo class and use the max-width property to resize the image to a smaller size.

I remember reading somewhere online that for every image that is being sent at a size that is above what is needed, a tiny bit of delay is added to the end user experience. I understand that this example is for learning purposes, but for websites with large number of supporting assets, the benefit of convenient resizing within the code may be outweigh by the cost of sending larger-than-required image file sizes.

Is this something one should pay attention to when in a deployment phase of a site design process, or is it not that big of an issue.

Thank you for your time, Taki