So, do you really need a rub for meat? I think that depends on several factors, namely the type of meat that you are cooking and how you would serve it. Here are some examples.
Brisket: If you are going to slice your brisket and serve it that way then yes, you should definitely add a rub. It will add a nice crust to the meat giving it a good flavor, appearance and texture. If you are going to shred the beef then no, you do not need a rub. I would add a bit of salt and pepper for good measure but most of the flavor being achieved will be from the smoke and you can season it later after you shred it if desired.
Pulled Pork: The same thing that goes for shredded brisket will go for pulled pork. No real reason to add a complicated rub if you are just going to shred it and mix it up. It would be the same thing as just seasoning your pulled pork later. With a cut of meat as thick as a pork butt, one could even wager that a sugary rub that caramelizes could inhibit smoke penetration, actually harming your final product.
Ribs: Absolutely, without a rub, your meat would lack flavor. Add a nice rub to ribs or at least salt and pepper if you intend to serve them wet. If you intend to serve them dry, you need a good flavor profile to compliment the meat.
Chicken: Just a little salt and pepper will do, no reason for a complicated rub. Whole chickens with skin on will not benefit much from a complicated rub, all that you want is to add a little seasoning to the skin for those that like to eat it. For everyone else, they will just be shedding the skin anyway so your rub would just be lost.
In Conclusion: Basically it depends on how you will be serving your meat. Sliced, then yes, the rub would end up intact and should be applied. Shredded, the rub will just end up all mixed up in the meat and you might as well just season it later.