lightshielding on the edge (of a platform) is almost always a good idea, you get pushed off the side and can react instantly (as opposed to a normal shield, where you have to tumble recover before you can act). Be that double jump -> ****, or a simple fair (with marth) its a good idea.
light shield takes alottt of stun. But its a good idea and works out alot. for example:
I always shine ooS under pressure
opp decides to nair -> shinegrab and i keep getting grabbed before i can counter
light shield means the shine grab wont connect.
the next stage of this mindgame is normally opp empty hops into shield -> shinegrab, and theres nothing you can do about it.
lightshield on the edge of the stage when a falco approaches you with SHL, by the time he reaches you, you would have bee pushed onto the edge. if he is not familiar with the mindgame, its a free attack from the ledge