I tell my camera to take the largest photos possible. Which means one photo crashes my friend's email server for being too big.
It's also great for posting photos to permies.com. I set the image to 25% of the original and it seems to be a perfect size. The image still looks awesome but it uploads so quickly now and the page is faster to load too.
That is useful to have a web tool available to resize photos.
For everyday use I would rather have a computer with software that doesn't require an internet connection. On Windows there is the free program Faststone Image Viewer, which also can bulk rename and do the best fast full screen sorting of any program I've found.