I don't drop animes. More like put them on hold. I don't have time in life to constantly watch anime, so if it's easier to obtain and watch one anime than it is another, or if one anime is more interesting to me than another, then I suspend the current one and jump to another. I don't actually like doing that though, but I do have a log of every anime I'm watching, what episode I'm on, and whether I'm watching sub or dub, as well as what site I'm getting them from. I've never had to drop an anime before because I think that's disrespectful, but to be fair, I usually look into the anime's plot prior to me watching it to see if I think it will be interesting to me or not.