Negative effect is less yield. Where there was once bud there is now a seed. I polinated my first plant a month odd back, due to not selling weed, it's nowt but a good thing. So i've taken to just leaving a male plant in my cab and let it pollinate the whole lot. Means i get lots of funky strains to play with, means i'm making new things and means i don't have to pay £5+ a pop at the seedbanks. Also means i get lots and lots of seeds to post to various people to enjoy meaning they no longer need to get ripped off by seedbanks either.
Quality is argued, a lot of litrature states that it get' more potent when eeded as it creates more THC to protect the seeds. Others say otherwise. Short story ebing that it doesn't appear to effect potency in any discernible way for better or for worse.