I've seen older blocks that the pieces were pieced.
I do not like to do that - but if that's the only way to eke out a block - i will do that.
For conserving fabric - before buying it - I try to remember to check to see if it has been pulled off-grain. I really have to be in love with the fabric to buy off-grain fabric. If it is a print - has it been printed on-grain? Sometimes it has been printed on-grain, and been pulled off-grain. That can be straightened. If it has been printed off-grain - it is off-grain. Deal with it - or not.
I do "assume" about two inches of shrinkage per yard of fabric - I am not sure if it will be lengthwise or crosswise, but many fabrics have shrunk about that much. So - even though I am not "saving" by buying a couple of inches extra, I am building in "enough" - assuming the pattern is correct and I don't mess up.
If I actually know what I am going to be doing, I try to lay the fabric out and "survey" it before starting to cut - especially if working with something that needs to be fussy cut or is directional or has big pieces.
Maybe for me, the biggest "conserving" is to plan ahead - at least as well as I am able to.