If you host your site in a poor environment, WordPress may fail uploading large images as the process of creating the different sizes and thumbnails takes a large amount of CPU usage.
With this Plugin the images are simply resized to a maximum dimension (of for example 1600 x 1600 pixels) right in your browser before uploading them.
The nice side effect is that unnecessary big images are resized to a fine size to still provide a usable, qualitative image.
Logo credits: Picture graphic by Flaticon from Freepik.