I'll preface this by saying that I don't jailbreak, though I have considered it.
The idea of jailbreaking is to let users have access to the iPhone OS file system, allowing you to do things with the device that Apple never intended, such as installing apps not published in the app store, usually those that do things that go against Apple's policies. That also means that legitimate apps from the App store can be installed without going through iTunes, which is usually thought of as amounting to piracy. Jailbreaking also allows the unlocking of iPhones to allow them to be used on networks other than AT&T (or whatever your country's sanctioned iPhone network is, Rogers in your case).
If you jailbreak, there's no guarantee that future Apple sanctioned software updates will work or they could (potentially) disable your device (brick).
People who have jailbroken their devices I'm sure can provide more info here.
Steve