I kept Unleashed installed because it did unleash the TS1 neighbourhood, by expanding it from the 10 houses we'd been limited to until then. Besides, it had a crazy cat lady, and since that's that my goal in life (I've got the cats, I've got the craziness thing happening for me, now I just need to learn how to be more ladylike), how could I resist?
With TS2, I kept Pets installed solely because of the carpet dividers. They were great, they acted like a fence or wall to stop noise, but sims could step over them. They were very handy to use around cribs so that crying babies wouldn't wake up other sims, and unlike fences or walls they didn't obstruct either my sims' movement or my camera view. I played a couple of households with pets in the first week or two I had the EP, but didn't find the pet aspect of the EP interesting enough to keep playing with pets.
No doubt there'll be some non-pet related reason that will make me want to install the TS3 version when it's inevitably released, so I'll probably get it. But not for the pets.
