Why YSK: If you have digital data that is important, (family photos, crypto keys/wallets…). Back it up and prevent permanently losing it.
3 different places its saved to, (iPhone, ICloud, laptop, Facebook, Google, Camera SD, Flash drive…).
2 different media, I would consider iPhone and iCloud the same. Buying two External Drives of the same type and brand too. Why? Consider losing your Apple account or the drive model fails in a year.
1 off site copy. If all your copies are in your house, a flood, fire, tornado, hurricane, EMP… would lose every thing.
0 time to waste. (My own personal add). Do it now. Procrastination is dangerous and is the biggest regret for when things go sideways.
Trust level can vary. Publicly shared photos I would suspect you’d be okay with. Your crypto wallet… less so. Everyone needs to work out what’s best for them, however, the original point is … don’t have all your eggs in one basket. Backup your data.