I, for one, like the fact that my different concurrent shells have
different histories (which have a rough correspondance to their
different current directories).  I'd be rather unhappy if I didn't
have two different histories for two different shell windows.

I don't care much one way or the other about histories saved between
sessions, though it sounds complicated when you have multiple
concurrent shells, if you don't want to have concurrent shells
sharing the same developing history.  (I've never really been clear
how that works out with bash, but then I only use bash once in a
great while.)

-- 
  "I probably don't know what I'm talking about."  http://www.olib.org/~rkr/