Generally speaking resizing works best for a few reasons:
1) Even if the broswer auto-resizes images that is done with default codes that might or might not apply sharpening to the whole photo. Resizing reduces sharpness, but if you use stock website codes your shots could end up over or under sharpened. Resulting in loss of quality.
2) IT helps those on a slower connection speeds.
3) You don't need to show fullsize; most of the time a resize is all you need to show because that's the whole photo.