If you own a whole bunch of DLC from The Sims 3 (as well as the base game,) extra items will show up in The Sims 4 as a reward. It’s nothing too amazing, and in fact mostly appears to be a set of vaguely thematic novelty lamps.
For example, you’ll wind up with an ‘Enchanted Aurora Award’ for owning the Supernatural expansion. The description for this one says “May this mysterious lamp intrigue your Sims in The Sims 4.” That probably means they’ll stand near it and make “oooo” type sounds, I guess.
Owning The Sims 3 base game provides the ‘Let there be Plumbobs Award’ (the green one in the picture above.) “Let this lamp light up your Sims’ world in The Sims 4,” the description on this one says.
You get the idea with that. Each bit of DLC you register through the link above will get you an award-lamp of some kind. If you own everything from The Sims 3, you can have the weird golden statue in the middle of the image above. It’s called the ‘Ultimate Freezer Bunny Award.’
The Sims 4 will be released on 2 September. This is what happens if you mess around with the Sims creation mode and things go a bit hideous.