If a small space was left (less than 1/4 inch or 6.4 mm) the bees filled it with propolis; on the other hand, when a larger space was left (more than 3/8 inch or 9.5 mm) the bees filled it with comb. The invention of Bee space in honeybee behavior has been very important in modern hive constructions. So keeping space between 6.4 and 9.5 will keep space where bees can easily move and the won’t cement it with propolis or consider it they should build a new honey comb.
Due to the observation of bees and recognizing bees’ space is constructed the first modern hive like LR beehives. The first in modern times who realized this was Lorenzo Lorraine Langstroth (1810-1895), creator of LR hive.