Images always take more time to load than the rest of the content. This causes CLS which impacts usability of the page negatively, as things shift around while it loads, and may deteriorate SEO ranking.

Imagine browsing a post with loads of images and you scroll down faster than the images can be loaded. Suddenly the browser goes

oh this image is this much wide and high, and the layout is squeezing to 700px wide .. 🤔 (browser doing some maths) ... so I have to push stuff down to create a 525px high space for the image.