I don't show, but I do clip all the hair out of the ears on two of my horses. Gnats and no see 'ems are horrible in my area, and the hair doesn't offer enough protection. I have to keep a layer of Swat or Vaseline in their ears at all times to protect them, and the combinatioin of Swat, long hair and dirt is just incredibly nasty. Also, with a clipped ear, I can see immediately if they need more Vaseline or Swat.
My pony's ears are so tiny, and the hair so thick, that the gnats don't bother him, so his I leave alone.
In the winter I just trim the long hair for neatness sake as others have suggested.