people will tell you different things, its a matter of opinion really but here's my rule of thumb:
if the leaf is completely dead cut it, if it is over half dead (wilted you know what i mean) cut it. anything that is still green for majority of the leaf it is a keeper.
i dont ever trim fan leaves, if im having a problem getting light to the lower flowers i just add more lights (around the sides and the bottom). fan leaves are a plants major life support, it is where all the photosynthesis comes from and is needed for your plant to live so dont go clip happy on the young lady.