timing belt tools - cant find the answers

[millertyme]

 <http://www.smileycentral.com/?partner=ZSzeb001> 
guys,
i have been reading archives here as well as other sites and cant find
the exact answer to the question of why do you need to lock the balancer
to remove the bolt?
 
from what i see, there is a key on both the crank and cam, and as long
as the timing is right prior to removing the belt, why do you have to
keep it from turning?  all that can happen, in my view, is that the
motor can turn over.  if this happens, the cam will turn with it, and i
cant see the concern with that happening.
could someone please clarify this for me.  thanks
also, does the front bumper need to be removed to do this job?
somethings i have read speak of jumping on the breaker bar.  how is this
possible with the engine in the car?
also, if it is truely needed, i obtained some measurements for the tool
2084, but am missing some particulars.
is the cut out for locking the balancer at 90 degrees to the length of
the tool?
what is the total length of the tool?
how deep/wide is the cut out that locks into the alternator mount?
i ask these questions because i have checked with local garages, and
parts stores, and noone in my area has the experience or tools to do the
job.
thanks
brian