CHOST should be left at what comes default, for most people anyway. The CFLAGS is what you should be editing. And no, CFLAGS isn't important, it just helps with optimization, you don't have to have anything there if you don't want to. To find out options for CFLAGS look at gnu's website for GCC as all the flags are listed there:
www.gnu.org/gcc (I think)
The CHOST is what your apps and everything are compiled against (for architecture) so that is important that it remain the same. If you change it to say, ppc and you are running intel architecture, then you'll be in a world of paper weights.
Cool