I got all EPs and SPs installed, except for Pets and University, and maybe I want to install Pets. Before that, I have a few questions about it, from what I read about it, so I hope you want to help me.

What will happen to the wishes of my Sims? Will Sims children always have a wish to have a pet? Since I installed BV my Pleasure Sims wants to go on holiday a lot.
I use empty templates (or, if not availeble, clean) and the walkbys in my hood are only Sims I created. Will the Pets EP spawn Townies, DownTownies or NPCs?
Any needed mods?

Maybe, after reading the answers I don't want to install the Pets EP anymore. But I thought: why not asking things, asking doesn't harm my game .

Thanks for the answers from a doubted Simmer.

when you first install the pets, your sims will get wants to get puppies/kittens/womrats/birds, but it won't be predominant...stray cats & dogs will be spawned (I don't use templates, so not sure how that would work) once sims get to know animals, either strays or the ones you adopt in, they'll roll wants to teach them tricks, wants to command them to do stuff or play etc. Which if it's for a pet on lot, makes for easy want fulfillment. Knowledge sims will roll wants to become a werewolf now & then.

First of all, back up your game first! If you decide to uninstall Pets, you'll want a pre-pets copy, because the pets you create are full characters, and if you take away the engine that permits them to exist, you're asking for trouble!

Second, add the Pets patch before you open the game. If you have Seasons you're probably already patched up; but there's a pregnant animal in the Pets stealth neighborhood who carries the same glitch cooties as Samantha Ottomas, and better safe than sorry.

Third, Pets adds NPCs like the Dog Trainer, stray animals, and wolves; and playables like Cyd Roseland and his dog Porthos, as well as containing two (safe!) occupied lots in the lot bin. If you don't want those added to your neighborhood, you need to use the same procedures you did to keep unwanted sims out of your existing neighborhoods. Read the instructions, I don't know about procedures for not loading the Kat and Kim families to the lot bin, but they're a special case and can sit in the lot bin indefinitely without impacting your game.

Fourth, yes your characters will start rolling pet-related wants. Family sims and children are particularly prone to wanting to adopt pets, Knowledge sims to wanting to hear howling wolves and become werewolves, Popularity sims to wanting to befriend pets they meet, etc. You'll also get new Lifetime Wants such as "Raise 20 Puppies or Kittens," "Have 20 Pet Best Friends," and "Have Six Pets Reach the Tops of their Careers."

Pets is one of those love-em-or-hate-em EPs. Just as in real life, don't let a sim get a pet who isn't going to have time to deal with it. Dogs and cats are individual, uncontrollable sims with needs and characters that have to be taken care of. Grim comes for them, they get relationships, and they behave well or badly depending on how they're trained and how well their needs are met. Birds and womrats are objects that require maintenance - they have to be cleaned up after and fed, and they provide benefits. The only way to know if what they add to the game is something you want is, to add the EP and play it for awhile.

@ TychoH > If you are worry about spawning of townies or Pets a good Mods to get is J. M. Pescado Notownieregen and NoStrayRespawn they are at MATY ( More Awesome Than You ) it is in his Hack Directory the one for Pets is under Pets look for whatever is the last Ep you use to start up your game. For me it is Seasons most of all his Mods are in that file, as in others depend on your last installed Ep. It work perfect Pescado it known for one of the best modders around.

Now about "Pets" I think you will love it, I have Pets in my game, having Pets make the Sims game much more realistic, as in real life. Not all Sims will have the want for a Pet, it depend on their personality traits, aspirations and zodiac sun signs.
Also there are Cheats to help you control your pet ( somewhat ) they still have a mind of their own. If you should download Pets into your game Be Sure To Get The Patches. ( important ) And as always back up your game before you download Pets. Incase you change your mind, that way you will have your backup before you added Pets to your game.

If you should download Pets I will be more than happy to share with you the Cheats for Pets the cheats came within the game, but EA fail to let the players know to turn these cheats on when playing Pets, so that we may have some kind of control with them. If you should or have questions I do have the Pets 2 Prima Official Game Guide. Just PM me if need be, or come here to the Sims 2 forum most members are more than happy to help.

Thanks everybody, your answers are great. I'm really happy with it.

I back up my game and then I will install the Pets EP and patch. After reading your answers I dare it .

There's also a No Pet Obsession hack so they'll stop rolling wants to get a puppy/kitten/pet. Can't remember offhand whose it is, either Pescado or TwoJeffs.

Pets is one of my favorite EPs.I love the cute things that they do Make sure that you get a dog toy or a cat scratching post as the animals will chew/scratch your sims' furniture otherwise.

@AlexandraSpears
TwoJeffs: http://www.simbology.com/smf/index.php?topic=12.0
Thanks. If the wants annoy me, I'll add the mod.

@Rarr
I bought that for a cat, but he destroyed the couch

I think I love the Sim cats. And I think I keep the EP installed .

Some pets need to be trained not to destroy furniture even if you give them a legitimate target, and some will never need training at all as long as they have their toy. Glad you decided you like them!

You may want clean templates to keep the strays, adoption pool, and bin families from spawning. Pescado's wants and fears sanity mod (wfsanity?) will keep sims with no or very low interest in pets from rolling pet wants.
One of my families right now has a cat that will NOT play with toys--if her fun is down, Yangtze ignores her bird and catnip mouse and goes after her people for attention. She does scratch her scratching post. Crazy cat.