it is indeed so that genkernel does more then you actually require, which makes the kernel bigger then you would require it to be.
Usually enough information is given when you press help on a specific option in the kernel. And it'll also give you advice on wether to use it or not. Allthough this is not true for all the options!
This is perhaps a rather usefull site, but again, most help given here can also be found by pressing the HELP button inside "make menuconfig" on the option you want to set.
http://kernel.xc.net/
Complete config for ex:2.6.23 on ex: i386.
You will get a complete list of all the options inside kernel 2.6.23 and if you press the HELP button next to it, it'll give an explanation!
Hoping that this will get you on your way,
good luck!