@ thibaut: Thanks for your explanation! I will return to being happily content to be a solo traveler.

We don't always have control on what gets checked.
We always cross pack. It is actually quite trivial, costs nothing, and significantly reduces the pain in case one luggage gets delayed.
We use pack-it cubes.
One pack-it cubes contains one complete change of clothes matching what we wear on flight. Each carries one such cube in the carry-on day pack/tote bag. This ensures there are four clothes combinations not matter what happens. That is four times the number of outfits compared to those who don't bother to take any delayed luggage precautions.
Then we each pack another complete outfit in a pack-it. We exchange this pack between us. It takes about three seconds. This ensures we have eight clothes combinations even if we loose any one luggage.
All others go into each one's luggage.
Why we bother even when we always (intend to) carry on everything? There are probably many who have never had to check their luggage against their intention as if such thing never happens. However, I have had my share of grim reaper gate agents walking around the boarding area with luggage tag requiring those with larger carry-on compliant bags to check their luggage because they expect the overhead bins to be full. We can readily give them our luggage knowing we are as protected from the loss as possible.
Those who have not thought about such possibility end up rummaging through the luggage extracting items they don't want be left int he cargo hold.
One of my work colleague went to Africa. His luggage got delayed but because he moved around quickly, so he was without any change of clothes for 2 weeks in Africa. That is fun.
My sister-in-law who believes nothing bad ever happens to her got separated from her luggage for three day.s She had to do with what she flew on for three days, in northern Africa.
A college professor, a self-proclaimed travel guru, left everything in luggage, because he never lost his luggage, until the last trip to Turkey. He did not see his luggage for one week. He also had to do with one outfit he flew to Turkey.

I had a colleague (and good friend), a very tall German woman. We went together, about 15 years ago, to an accademic conference in China, where we both had to present papers. Her luggage went astray, and didn't turn up for the duration of the conference. She couldn't find any clothing in Beijing for a woman of her height, so she ended up buying several pairs of men's pajamas, which on her were Capri-length.

Kja, he would definitely sneak into my 'side' then try to squeeze in an extra pair of jeans, LOL. I like to control my space.
Heading to Germany tomorrow, with my smallest check in bag ever. Minimum clothing changes, but I wash en route (while showering). Travelling with my father this time, he has taken up my challenge for travelling light, but I am carrying all the gifts for family, so not quite an even contest.

We always cross pack. My husband amasses all of his clothing, folds it and halves it, I basically do the same, we put in 2 suitcases and it’s done. We do take a shirt/blouse or two along with undies and jackets, depending on the time of year, in a small carry on or backpack along with meds, etc. and yes, 99% of the time we check our bags.