Hi Avatar,
What makes you think that?
Love,
Carson 
becouse, energy flows in and out of the 9 opening with every breath.
the anus, the front of it, is were the spine ends.
mulabandah is tightening the anus.
think of it like this, instead of not being aware of the flow of energy in and out of the anus BUT using the root lock, or siddhasana. and just taking to the sexual organ.
you incorporate its flow, and effect the body of the spine twice as much.
its just a thought for some of you, itl either be usefull to you or wont. but remember, as the nostrils flair with pressure, as above so below, that is a sign of movment in energy. good luck with it.
just made me wonder, why do we only work with one of two of the lower gates? will not both help our work? they are the ONLY two lower GATES. we use one to rise, why not the other. haha and it figures, the 8th governes the spine. but i may be wrong! 
and ive been using it, workd good with spinal breathing.
but i am still trying to master my perticular way. the fire path as apposed to spinal breathings water.
dunno sumate. not a master of it yet.
Do the full yogic breath.
in the abdoman, stomech,chest. full in.
at the end, the belly should be back a little, due to the rise of the chest.
hold, til you think about 65 to 50 percent of air is absorbed.
not more than 3 secs. this parts up to you.
then exhail breathing pushing the stomech stomech back and breath in right away.
this is a 2 parts inhail one part exhale. get rythem and be consistant.
if you start to get cramps, or persperate, stop. the key here is not to excite the body, as soon as that happens, your body starts to absorbe chi. and raw prana wont manifest.
if your doing spinal breathing, and you have a great pressure. it may be possable for u to make the exhail go down and out one of the two channels down their. thats right, pressing the pressure out then bringing it back in. but i have found
“while using immense pressure strong enough to make full erection turn to no erection at all” that it didnt work well. of corse, i also did not, while i had this pressure, experiment with the channel of the anus. so that may be somthing ti try.
raw prana, this vibrating. youv felt it befor, the thing is learning to do it.
first time i experianced it, was expremly rapid full breath.
but i had a double fold downwards sexual flow.
it is said, the vibrating of life force, comes from stimulating outflowing chi, but i dont believe its right to focuse on that aspect of it.
but whatever works.
ever feel the slight buzzing of the hands, same difference, except im talking about raw chi in bulk.
you have convinced me, to make this my second priority.
the first being the refinment of the fire path method.
the second, being mastery of raw chi, so that i can explain it in such a perfect way that we can all do it. that part will help water and fire paths.
and yes, i know yoga is usually called fire path, they are all fire path. i simply call it like this, cause it seems like. well.
i take it back. its ignorant to call either one that. since both require fire in order to turn water into air, and gain chi from it. chi/vitality.
actually the last time i experianced this fire, that turns water into vitality, was threw using spinal breathing. haha.