seems and baking normal for games

hey so say you have mesh number 1 and that is an object that is more square and man made and not a natural object. lots of hard edges and stuff. and then you have the exact same object just with sub division mod. i hear people say its a must to put a seem around all hard angles and edges. is this true? i must say ive always had troubles with baking and ive tried different things but never had good results. always been really bad at it. but i want to know if this is the best way to do it.