Does jailbreaking the IPhone 5 slow it down?

Some people say it does and some people say it doesn't. But does it really slow it down or it only slows down if you install too many tweaks

All your doing is breaking the security apple put in place to keep people from customizing their phone they way they want it. It adds an app called Cydia and does not slow down the phone. Now some people start installing apps from cydia without knowing what they do and can mess up the processor and slow down the phone, or run very CPU heavy apps and slow down the performance.

Simple Jailbreaking it will not slow it down.

It breaks your security on the phone that Apple has placed in each firmware update. The more you install tweaks, the more it will slow it down. Plus, Cydia (I think that's what the Jailbreak thing is called that's installed after it's jailbroken successfully) is run by professional hackers. There have been many occasions when they have hacked into people's phones/iPods/iPads while running Cydia. I've jailbroken an iPhone 3G, and my brother's iPod and the iPhone is stuck in the 1015 error code, and even professional smartphone repair shops haven't been able to fix it, and I've been to three different ones; I've also tried about 10 times to fix it on my own, but I now have the iPhone 5. The iPod dies after about 5 minutes of use with a 100% battery charge, and doesn't charge half the time. Oh, and don't jailbreak it because that's opening a great phone up to hackers.

-- All jailbreaks are created by hackers, at least the ones I've used and later found out. Jailbreaking really isn't the best thing to do, just to get what you want on to it. Just pay for whatever you're trying to get, or just don't do it at all. You're better safe than sorry for wasting $200-600 (depending on what carrier you have) on a phone that ends up either hacked, or stuck on an error code.