I just had a discussion with my FS about what to do with frozen embryos and she suggested, if you weren't morally against it, keeping them in the off chance that medical science comes up with a way to use them to assist the children you already have if they ever need it. I guess like to grow a lung or something. She said that because it would be genetically similar it could possible be used like that. Seems so Sci-Fi but I guess thats what everyone thought of IVF when it first came along.

But I suppose that is only useful if you can keep them for an indefinate length of time.