What's the exact difference between previews and renders?

[justavisitor]

Does anybody know the exact difference between live render previews and actual renders?

As I've said previously, I'm trying to find a way to save an animated sequence in preview render quality, instead of 'real' renders.

For some purposes, such as hair, live preview renders are more desirable: They look smoother, softer and more fluffy - and they take only 30-50% of the time to render.

But if it isn't possible to save these previews (other than to actually make screenshots of each frame, which isn't particularly funny when you have to do it 1,000 times), I would like to know if it is possible to emulate the live render preview look in a 'real' render?

[justavisitor]

To clarify the difference between live preview and actual renders, here are a sample of each:

The one above is the 'real' render - the slightly blurry one below is the Preview, both @ 100 samples.

It may be a bit hard to imagine from these samples, but the full version of the Preview does look fluffy and hairy, while the render looks more like a haystack.

Which is why I'd prefer to go with the previews...

EDIT: It would, of course, be possible to make the real render more fluffy by decreasing hair sizes. But the project is about one GB already, and again; the previews are fast and they do have the right look, so it would be great if it were possible to save them. Or find a way to emulate their character (and render time) in the real renders.