Apologies if this is a rather basic answer, I’m sure others will be able to expand upon or refute any of my points presented here. Hopefully others will also bring up those that I didn’t touch on. The more arguments available, the easier it is to see a clearer picture on a certain issue. I realize I only presented 3 points per argument for and against, and that may not be enough to satisfy your needs. However, I hope it helps.
Although I’m mostly in favor of federalism myself and I’d like to see a federal system adopted in my own country of the UK, I don’t wish to influence upon your own view too much and that’s why I presented both sides of the argument. These points are the ones I generally had in mind, and others that I may have forgotten now, when making up my own mind.