ehhh?
They save as much weight as putting light tubes in your tyres, unless you can be bothered to change them again when you get home.
Why wouldn’t they go in a saddle bag, that’s what they’re there for.
Michelin Aircomp ultralight, not the latex version. I tried Conti supersonics and kept ripping valves out of them, the Michelin are 20g heavier but never had a problem with them. Fairly cheap and available at Decathlon too. Not (deliberately*) tried anything else so can’t comment, but the Michelin are as light as they come without going for the supersonic or latex tubes.
Some people get on fine with latex tubes, the constant topping up and puncture risk annoyed me.
*I’ve probably used most others at some point as they’re what a shop sold me, but I’ve never ordered anything else.