Pros: access to custom firmwares and programs, vastly extending the vanilla console features. For example Bluetooth audio worked years before the official Nintendo patch. Other notable examples: tweaking device performance (CPU/memory), game saves manipulation, webbrowser access.

Cons: don't use it online (including browsing or gaming) or accept the risk of potentially getting the console and the N.account permanently banned. Game and console software updates require special commands. Custom firmware and trying things out isn't particularly easy for non-technical people. Bad manipulations can permanently brick a console, turning it into an expensive paperweight or door stopper.