if you want to delete and and have more space for anime you should do it, the torrent will still be alive even there are no seeders but the download is super slow, i read this from a website i just dont remember what site.. there are many leechers in the torrent world especially in public torrent trackers so its not fair if your the only one who will seed and others will keep downloading from it unless you really want to share the anime you have.. another way of sharing is to upload it in a free file host like mediafire, megaupload, etc.. what i do in torrent, i limit the upload to 3 kb/s per torrent in the completed downloads and when i need to delete it, i just do it without hesitation.