It is not something that had occurred to me as an application, but our new freezer has come with a couple of 1200g phase change ‘Cold Storage Accumulators’, which
1 - act as protection during power cuts etc.
2 - provide a buffer when adding a quantity of food to be frozen.
3 - can be placed in contact with food for quicker freezing.
A very obvious application, which had completely passed me by - possibly because our freezers tend to last more than 15 years each.
Have these been a common thing for a long time?