@amaranthin: I'm not hazelnut but I have done some cloning. Some are precautions, some are cool notes, room to add stuff for sure.
1. The feature is a guarantee to getting facial clones of sims and the only outcomes are perfect facial features and good/bad/neutral traits. Yes this was really a fear I had when the feature first came out. But if you're really attached to a hair or eye color in a sim, those are often changed during cloning.
2. The samples you get actually don't contain any data from the sim. They are essentially placeholders that say "get data from this sim when you try to clone from me". So a problem arises: what if the sim in question dies but you didn't know them well enough to produce a tombstone? (friendship or enemyship at death pretty much guarantees this) Or what if the sim moves out and is essentially deleted by the game? It's bad news for your samples. Maintaining friendships with your donors is crucial to keeping those around. This is also why I'd get some backup people instead of the bare minimum of five or so.
Yes I know sims moving out of town is tragic and with EA's story progression there's no way to prevent it completely but I had a breakthrough kind of recently:
the game will not cull your coworkers. I have played a lot of games and the only things I've seen coworkers do is become homeless (unless I wanted to impregnate them: whatever) or die of old age (inevitable). If you have enough working-age adults in your house at the start, you can be smart and target the pre-mades you like the most.
3. Do not travel with DNA samples because the link to the sim will be lost. Do not bother getting DNA while abroad because it'll be lost when you return home. The samples will still be there but they won't have a name attached. You can place them on the ground and they'll likely be undisturbed (I always have a basement room for this) and once you can travel and get a chest from a World Adventures location (hopefully without your DNA in tow), those are invaluable for literally everything.
Now supposedly you can collect DNA from foreigners/uni students if you invite them to visit you and you take them at home. There is some data about visitors that's kept at home. But I heard it from a user that left years ago and literally no one else.
4. Funny enough you can collect DNA samples from ghosts and the resulting clone won't be a ghost. And it's not banned for the Immortal Dynasty? My reasoning is twofold: you still had to put in the work of staying friends with them to have a ghost in the first place (unless it's a pre-made and you still have to be friendly enough to get a DNA sample from them) so this isn't really cheating, you're putting in about the same amount of work plus waiting for them to haunt in the first place. And finally, I found it out by doing it in an immortal dynasty that I didn't wanna fail.
5. You can't get DNA from sims with the Neurotic trait but a Neurotic sim who gets to Level 8 in the Science skill will get two complementary DNA samples from themselves.
Also this is unrelated but for whenever you reach the conundrum of who will father the last generation, I have one semi-viable alternative to getting out the ghosts: at the start of the game, befriend as many male service NPCs as you can. While service NPCs age they sometimes won't die unless you summon them into the world on a day you're warned about their death. And there is no way to really litigate it as a dynasty moderator. Like do I force you to invite people over so they can die? I'll pass on that. Anyways you either have a cool living boyfriend for Gen 7 or you have extra ghosts and win either way.
