What is the advantage of one ultra-low cryogenic freezer

Here is an interesting experiment. Firstly, we need two bottles of water, and then use a marker to mark out the height of the water surface respectively. Next, we put the two bottles of water into the ordinary refrigerator (-18℃) and the ultra-low cryogenic freezer (-40℃) respectively. 8 hours later, we found that the water surface in the ordinary refrigerator was 1 cm higher than before, while the other one is almost no change in the ultra-low cryogenic freezer.
   What is the reason for this? It is because the water crystallization period time (0 ℃ down to -5 ℃) is shortened. It makes less air into, so the volume will not increase significantly. Therefore, when we storing foods, reagents, specimen samples, the crystallization period of water in the cells is shortened. The volume of things which are stored will not over excessive. Then the cell wall will not burst, which is more conducive to ensure the taste of food and ensure the activity of biological reagents.