When uploading a lot of images to a server, to minimize the space taken by the images, is it better to resize the images before sending to the server or upon resiving them?

It seems to me that resizing them in javascript can take long time for not a lot of gains. Is there any value to doing it on the client side?

EDIT:

The backend is JAVA and the server will have multiple users at onces possibly loading images and other files to it.