Bandboxing is implemented tactically based on strategic information and dynamic circumstances. I'm some instances (for example, EDUU) elementary sectorisation is mandated as standard at certain times and with certain traffic conditions.
As an example, take a flight from Dublin to Newcastle at 190. With a traffic load of 1/60, every sector with a rate of 1/60 could conceivably be bandboxed.
The balance between capacity, demand, load... and controllers... has to be maintained. Where it's more efficient to operate elementary sectors rather than collapsed, then it's more often than not done.
