Truthfully, I don't know. Till now I've just been playing on an old Compaq keyboard lol and my mouse is a logitech mouse with two buttons on the side and a scroll. The only games where I could wind up needing the extra buttons is like Legend said in MMORPGs. I'm currently playing Star Wars: The Old Republic and I have a minimum of 25 keybinds. I use 1-6, Q,E,Z,X,C,F,R and shift+ Q,E,Z,X,C,F,R... Also, the 2 side buttons and scroll button are invaluable to me here because I use them for another 6 of my keybinds. I have gotten used to this and it serves me very well for the most part but truthfully there are some minor or extra abilities that I simply have a hard time keybinding because after 25 or so keybinds it becomes difficult for me to make more that are comfortable for me.
I've been wanting to try out one of those Razer Naga mice with all those buttons but I dunno... I'm so used to this already and I don't know how I would do with that mouse. As for Macro keys on the keyboard, I've never had those either but I guess it couldn't hurt right.