A potentially stupid question about recording in 24-bit with these new 32-bit interfaces

If I record “only” 24-bit with these interfaces, how does that work behind the scenes?
Does the interface only actually convert to 24 bits (I assume there is some kind of delta-sigma frontend anyway?) or does the 32-bit signal get truncated or dithered down to 24-bit?

And, most importantly, do I need to care in any way? (as in “a 24-bit recording with a 32-bit interface is somehow inferior to a 24-bit recording with a 24-bit interface”).

I’m just interested from a technical point of view - I won’t hear any difference anyway.