to further expand on your question, you really cannt and shouldnt make generalisations, because even from cue to cue from one maker or brand, you can and will encounter many different balances.
you should first start out with comparing what you have.
set a piece of chalk on a table or something and lay the cue fully assemled on it until it is perfectly balanced (neither tip or butt touching the table top). now measure from teh end of the but cap up to the middle of the chalk. that is going to roughly be your balance point.
i actually use 2 lengths of staples as they come packaged in the box that i wrapped a piece of scotch tape around to not damage the finish. it provides for a more acurate measurment as its thinner than chalk, some people use thier index finger, but its hard to mearure while holding a cue, but whatever works.
typically, for a 58" cue (29" shaft and 29" butt): 19" and up is considered forward balance, 18"-19" is nuetral and less than 18" is rear balanced.
for every 1oz added/removed to a side of the cue, it will move the balance point roughly 1". so if you have a 19oz cue with a balance of 19", and you add a 1 oz bolt in the butt, it should move the balance to 18" while increasing the weight to 20oz