Even though it's generated sender-side, AFAIK, you wound't even know it is there as a feature. You paste a link, wait some time, and a preview appears. If you send it immediately, there is no preview. Which is acceptable, but at least give some kind of indication that the preview is being generated. Or for some links there is just no preview, and you stay there like an idiot waiting for a preview to appear without any notice it failed. Sometimes the preview is just not that good, although it's also up to the link optimisation.