some people pefer to use a boom vang to hold the mast rotation when sailing down wind. other people will use a vang as a kicking strap to stop the boom lifting to high during a jib. it is still a useful item on a mossie. even if other people dont use one at all.
it is up to peoples own opinion. and i use one. and so do a lot of people.
but do come to thr training weekend there is always plenty of help and advice.