Each insulin specific insulin group has an approach really due to the size of the group. Lantus/Levemir has a lot of active members daily, same approach is used to let people easily spot potential problems. Single posts drop other posts that might need help further down the list too. If all daily posts are in 1 place, it's easy to find later and easier to see cause of potential issues. Daily posts are highly encouraged.
Smaller insulin specific groups sort of follow that protocol sometimes but I don't know exactly what each one's detail is. Maybe others can give you more details in those...